Concerning insulation, your ceiling is the most important, followed by walls, then the floor. Of course you dont want loss or gain through windows, doors, mechanical protrusions, etc as well. A start would be to blow cellulose in the attic. This is diy friendly and most home centers will let you use the blower when purchasing the cellulose through them, or you can rent one. You want to be careful not to block any soffit/eave venting and be careful around any canned lighting you might have that isn't rated for insulation contact. Concerning walls, it is possible for insulation to be blown in the stud cavaties either on the inside or outside depending on cladding type. It would be bonus if you could have a reputable siding/window/door outfit foam board the outside walls and install newer efficient doors and wndows, but we are talking about some big money here. It never hurts to get estimates from a few outfits in your area. The floor joists could be insulated, or the paerimeter of the crawlspace insulated with 6 mil visquine spread over the crawlspace ground. They would also insulate on top of the crawlspace stem walls where the rimboard sits. You might want to get estimates and ideas from reputable insulators in your area as well. Ask others what they did if they had a similar situation, even neighbors who are in houses built same time period as yours.

What Sierra said plus:

Before you blow in the attic you want to seal the attic where any walls, electrical, plumbing, etc. penetrate. Use a combo of tape and plastic, spray foam and caulk. As Sierra pointed out, keep the soffits clear.

You almost can't put too much into the attic but a load is no good if you aren't sealed off.

Attic is number one and probably the least expensive to do, albeit a bit sweaty.

Here is what I've done over the past 20 years, taking advantage of good sales when I could and doing what I could myself: just as suggested above, first attic insulation. 1)I had the blown in stuff in the family room addition attic, and since I was able to get a really good buy have 2) put in a double layer of r-38 fiberglass rolls in the attic. 3) I later replaced the 70 year old metal frame windows and made sure they were well caulked (that REALLY paid off, too) and 4)added the spray in foam insulation into the exterior walls. The windows and wall insulation were the big ticket items, but I got a good price by contracting them together. Shop around! I shopped and planned for well over a year and got a really good deal. I think all those salesmen have me on some kind of a list now though.
The family room is just over crawl space and the floor was always drafty cold, so 5) several years ago had some more of those R-38 rolls installed under the floor between the joists, and 6)used the spray can of expanding foam stuff to seal around the edges of the floor and around the ducts. That helped a lot. 7)Put in much better seals around the doors. And made a draft stopper for the chimney 8)Lastly, 2 years ago when I needed a new roof, put in a powered attic vent. A noticeable difference in the hot upstairs after that. 9) Nearly forgot the ceiling fans in the FR and Bedrooms. 10) I am lucky to have shade on the south and west sides of the house, too: the pear tree that was only 6 feet tall when I moved in now shades the entire south face of the house.
Even in the very hot summer we have had here in central Ohio, I have had the A/C on less than 2 weeks so far, as much to dehumidify as to cool the house into the low 80's.(I'll confess that I like warm and don't really like the feel of A/C! Today it was 90 but not muggy--and the air did not come on at all)

In winter it is much more comfortable from eliminating lots of drafts and leakage.
Next time I win the lottery I plan to add the radiant barrier to the roof rafters, which should help in summer and winter. I want to cut the bills, but I want to be comfortable just as much if not more which is why I will spend the money although I may not see significant savings at this point.

hire an energy rater to give you specific to your home info.
what my years of this type of work have taught me is that
the air sealing is the first line of defense.
a blower door test will show you where your house leaks
and a duct test will show where ducts leak.
in new construction nationwide there is 25 to 30% duct
leakage in new homes..in existing homes it can be higher..it can also be lower..but not often the case.

caulk..not great stuff will provide a good flexible seal that will last (depending on years of caulk purchased)
great stuff breaks down and does not expand and contract.

if you can stop the air leakage into your house it will be
affordable to heat and cool

once the air barrier is complete then insulate.
insulation slows air movement but doesn't stop it
(except foam insulation which when properly applied
lowers air infiltration..for a price)
when air moves through insulation it lowers the performance
of the insulation.

when you put a power attic ventilator it pulls air from inside the house (at air leakage sites) and from ductwork
located in attic (duct leakage sites). pav's can put the
house under a negative pressure causing the house to pull
in air via holes ..recessed cans..the oversized cut for the drain under the tub...many of these leakage sites allow
voc's into the house which contribute to allergies ect.
cellulose insulation has a fine powder that spreads
through out the house..entering through leakage sites
and spreading via hvac system.

caulk caulk and caulk.
your biggest payback is reducing the air infiltration.

after that the duct/return air leakage

then would come insulating attic..biggest savings

crawlspace..open cell foam not batts. batts droop over time due to gravity..and condensation forms on the undersides of floors causing floors to rot. as wind sweeps the batts it robs the insulation of R-value (you should see a thermal
scan of batt insulation in floors on a windy day!)

then lastly walls.
air seal walls prior to insulating
caulk ceiling moldings to ceiling and wall
floor moldings to wall & floor
window and door frames to walls
gaskets behind plates of switches and outlets.

There is a national association of energy raters
hire one to evaluate your home and give you
real world proven information for your home.
www.natresnet.org
we are trained, nationally certified unbiased professionals.

best of luck

My parents had the walls of their 1958 home re insulated with blown in cellulose (pretty sure it was)about 8 years ago. They were able to access cavities in walls in most places by removing small section of the cedar shake siding, cut smallish holes(1 1/4" or so) to get in between each stud space. There were a few places they were unable to access that way, under windows on front of house that is brick faced 1/2 way up. For that they had to do holes under the windows on the inside in drywall, which they patched. Their heat bill went way down. In one room I found a small amount of frost on the inside a very cold day before they had this done.

By the way, this is in Mn.

WOW all ! This is a lot of information to digest and I DO appreciate every response ! Thank you all so much. I forgot to mention that I live in Myrtle Beach, South Carolina where the heat is high and the humidity is even worse. Most days this summer has been from 105 with heat index to 115. A very, very rotten summer. I have ceiling fans in every room but the best I can hope for is keeping the indoor temps around the outdoor temps. Sometimes it works, most often it doesn't.......

I'm working on insulating 1 room at a time right now because the drywall needs replaced anyways. I did notice that our little girls room which I finished yesterday with insulation and new drywall was about 10 degrees cooler than the rest of the house. Her BR door had been closed with the ceiling fan on and I couldn't believe the difference !

Guess my next step will be to blow in a lot of insulation into the attic and continue sealing around my windows (new doors have already been done).

Thanks again all for ALL the information. What a nice professional group we have on here !

regards all !

energy rater in la--Which I'd known that about the batts in the crawl space. And the great stuff foam. Great post, thank you.

Yes, I've noticed big payoff from caulking and sealing.

The attic vent doesn't run in winter, and I guess it hasn't been a real issue about pulling air from the house in summer since it allows me to avoid using the A/C.

Supposedly it will primarily pull air from the soffit vents to cool the attic and reduce heat into the upstairs... (I do know now in my smallish house, that the vent is oversized for the attic and the whole venting system is not correct since the roofer also put in ridge vents. I relied upon him and did not do my homework first. So in my situation, the power vent is probably NOT the best choice but seems to have worked out so far).

erthmun--All the ceiling fans do is make you FEEL cooler, they don't reduce temps at all. Although I notice that in some rooms they seem to help the warmer air go out the window.

Good luck with your projects, it will pay off.

Goegraphical location plays a huge part in determining what works in your area and what doesn't. You can have all the responses in the world about what folks have done with their home. It might or might not work in your area, ( unless they happen to reside in your area). Getting a consultation with pros who know what works in your area would be a good start.

raee
caulking & sealing my house made a huge difference also.
made a believer out of me..and launched me into my
current field of work.
its a learning process isn't it!

sierraeast is right..what works for me in my
hot humid climate isn't always what works for other
climates. each state has info at dept of energy specific
to that locale.

Would a dehumidifier, placed as centrally as possible, help make the home more tolerable during these lengthy high humidity periods? As an interim measure, not "instead of" the sealing, insulation, etc.