Agree with the PP: this is just like any proposal for work. Write out exactly what you want the contractor to do (specifications). Start with demo (remove and dispose of existing floor tile, cabinets, appliances, south wall, window, etc.). Also, what you want to keep (protect in place floor tile, window on north wall, etc.). You may want something removed and stored until the work is done (remove and store refrigerator in garage then install in new location).
Then state exactly what you want constructed ( construct new south wall as shown in plan, install new gas line and 220VAC for range as shown on plan, install tile floor at 45 degree diamond pattern, etc.). State if other contractors will be doing work on the site (cabinets to be installed by Sam's Cabinets). State what materials you will be providing (install ceiling fan to be provided by owner) or what materials you want to contractor to buy (install Kohler faucet KDR 778, install white electrical outlet and switch plates covers, install Cambrey tile 18x18 inch dove gray # 4689 with grout #224).
Once you have all the specifications, materials and plans completed, make copies and have several licensed and bonded contractors give you a line item bid (price for each item). Check with the BBB and the state that they are in good standing. Get a price and schedule from each of the contractors and pick the best (not necessarily the cheapest). Talk to neighbors, coworkers, church lady, etc. that have remodeled lately. They can recommend or "stay away from ___ " local contractors.
Always budget for 20% over the estimate. Contractors are not responsible for "unknowns" such as opening up a wall and there is mold, or older house and there is asbestos tile under the existing linoleum. Talk with the city to see if you need permits and who will pull the permits (owner or contractor).
You do your homework and the project will come out better.