Sorry to be one of the naysayers, with our first project we did it by the book, had a contract, checked references etc... and it was a disaster - builder from hell we ultimately had to fire, sued and won but never got a penny as the company folded.
I was even smarter the second time and asked for recommendations- ended up going with someone who struck out on his own and was recommended by a big and well known company (ours was a smaller job). Again a disaster - the guy went off the rails during the project, I think he had a drinking problem. The only thing we did better this time is we were paying in arrears and had a lot of money for the last payment, which meant that after getting rid of him, we had enough left to pay someone else to remedy the work (including leaking pipes and uneven floor in the bathroom so we had to rip the en-suite shower out and redo the floor as it was leaking through 2 levels to the kitchen and impossible to install a shower).
We now have used good builders for 3 projects - two small and one biggish. I would use them again 100% but it’s not to say it was perfect.
My advice, beyond the obvious, is therefore: make sure to check several references, get a referral, make sure that payments are not too front-loaded, and ideally, get someone independent to inspect the quality of work (I have paid an architect and structural engineer extra for that) throughout the project.
Best of luck,
M (please PM me if you would like our builders or structural engineer or architect recommendations)