Keep some spare tiles and timber is my suggestion.
When buying things like tiles and paint, buy a bit extra at the beginning and ensure it is all from the same batch number. It is easier to have an extra box or two of tiles so that if there is some unexpected breakage the trades person can continue instead of waiting until you source additional stock.
Make sure you keep them at the end of each stage. You've paid for them.
Tradies jump from job to job and if they can't work at your house they will quickly move to another job they can work at and get paid. They will then need to get back to you and in the mean time your house is delayed.
While it is up to the builder to organise this, they also have their own priorities. It's money, not necessarily your house.
Look after your relationship, the frustrations of dealing with builders and the inevitable issues that will arise can test the strongest relationship. It's no use having your dream house if you don't jave your your loved one to enjoy it with.
Have one person as the designated contact. The builder, tradies etc will want quick answers to matters but resist the temptation to agree to a change, even minor without understanding the full implications. They will quickly determine who they can convince to get something through that is not in your best interests.
Get everything you agree to in writing. before you proceed. Even an SMS to confirm that you have or haven't agreed to a change and any additional expense it will inevitably incur.
Document everything. Keep a log of what was discussed and what was agreed including any expense or changes to the project.
Have your per-determined unchangeable items, and what you will negotiate on if required.
Again, look after yourselves and each other, and please share the progress with us as it proceeds and hopefully we can all attend the house warming party.