First thing to do is get your mortgage in principal sorted, before even looking for a property!
Even then it doesn't mean much these days.
I had a mortgage in "principle" sorted in May, placed an offer which was accepted, put in 25% deposit on a 300k house, and then the b******s at the bank decided they needed more deposit off me, which I couldn't have provided at the time.

Lost my dream house, just because the bank decided that it was too risky?!
I had the perfect credit score, little outgoings and savings to show it. And despite my rather large deposit, they wanted more!
