A recent article on Style at Home, pointed out some really gret tips on how you can avoid mistakes when doing home renovations. You can read the full article online, but here's the summary:
Prepare: a detailed plan will not only keep you on budget, but on time as well. Also be sure to have written agreements with any and all contractors you hire.
Buy materials after planning: never buy any materials for a renovation before your entire plan is fully established.
Don't ignore any issues: especially important when you live in an older home, if you uncover plumbing or electrical issues during the renovation process, ensure you deal with them.
Take your time: don't rush a renovation just to finish it on your proposed time. Cutting corners will only lead to more problems and more money.
Careful who you hire: never deal with an unlicensed or uninsured tradesperson.
Don't do it all yourself: while you might think doing it all yourself will save you money, chances are outsourcing to a professional for a lot of things will actually save the most time and money.