Houzz just ran an article about this two days ago.

https://www.houzz.com/magazine/how-to-map-out-your-kitchen-remodels-scope-of-work-stsetivw-vs~1745902

1. Full demolition, removal and disposal of current bathroom.
2. Repair any damage or shortcomings found (rot, water damage etc). If damage is found, a discussion of what has been found and the cost to fix it should happen. This could include problems with plumbing or electrical which can turn into very large invoices. You want to know going into that if those types of costs may impact your total budget for the project. Keep some contingency aside for this type of issue.
3. If you are working with a designer, then ensure lines of communication are open between the contractor and the designer.
4. You'll need to decide if you are buying the fixtures or if the contractor will provide. If you have chosen, then full specs for the items you have chosen must be provided. This is something your designer will do if you have one.
5. Hire all trades and subtrades and settle all invoices etc related to trades/subtrades. (plumber, electrician, tiler etc)
6. You should spec any specifics about tile layout, grout colour etc. Those should coincide with vendor specs for the tile. (By this I mean if the vendor calls for no more than 1/3 offset for layout, then you should comply with that - not something different) If the tile calls for sanded grout vs non-sanded grout etc. For grout colour - best to choose it in concert with the designer or tile setter if possible. If you leave the grout colour choice to a tiler you will get his (or her) choice, which may not coincide with the vision you have for the bathroom.
7. Ensure your contract includes final inspections and sign off by yourself. Once all items are completed to your satisfaction, only then do you pay the final instalment (15-20% or so would be the normal hold back).
8. When I am working on projects with a contractor - I always put together a binder which our previous contractor called "the bible". In there I list all the items that have been purchased already, where they can be found if they are being stored on site, and wherever possible, pictures of the layout or finish (tile pattern, trim details etc) detail that we have planned. In the binder I include paint colours and sheen choices, and examples of trim pieces and styles that we want.
9. Always try to maintain good communication. And wherever possible put things in writing. If there is a discussion about anything and something is agreed, follow up on the conversation with an email detailing the decisions made. This is key if something needs redoing later - you will have the details documented for both yourself and the contractor to refer to.
10. I would also ask for regular meetings with the contractor - to review progress.....are they on schedule, is there any thing that requires a decision to be made, etc and at those meetings I would take pictures and notes, then treat it like meeting minutes and follow up in writing on any decisions made (point 9).

I'm sure I've forgotten some items here.....but this is a start. No doubt others will come along with better ideas and advice for you as well.

Retainer for design.

Design.

Materials selection and sourcing.

Deposit for contractor scheduling.

Materials Ordered

Home protection.

Demo

Disposal.

Remediation

Framing.

Rough Plumbing

Rough Electrical

Drywall and tile board

Tile

Tile

Tile

Drywall

Paint

Cabinets

Countertops

Finish Plumbing

Finish electrical.

Touch ups.

Punch list

Wine.

Need a pic of old bathroom and exact drawing. It may not get a new design....

Show the bath you have. A contractor is not your designer. It's 25 years old............

Let's guess: ?

Your shower is quite small. You have a big tub under a big window. Might even be in the corner.

You enter your closet through the bath.

There is a seven or eight foot oak or cherry vanity.....and all of the tile is either white with an accent, or it could be beige..? Am I close?

Whether or not I am, isn't the issue.

Post your bath in pictures, every angle possible.

Draw that bathroom on paper and to scale and note dimensions, for every wall, window, door passage etc.

Why? Because unless you already have the "design"? Neither you nor a contractor can bid.

Will plumbing move?

Will a toilet move to a better locale?

Will there be a tub, one coming out and new coming in? Etc.................and on and on.

Or?! Every single fixture and every bit of plumbing is staying in the same place, and all you want is new every single thing. ........

They are quite different in scope, and in labor price .

Show what you have as I said above, there's a lot of help on this site that far exceeds the design "talent" of a contractor. That guy is your technician.

Add inspo pics as well.