Never leave your fabric choices unattended held for you by the register, even if you have asked the clerk to watch it for you. Once it all got put away and I had to go and find it again and once it was taken by another customer in line. I learned that one the hard way.
Don't feel guilty about taking all of what is left on the bolt if you need it, even if someone is asking if you are taking it all. After all you were the one who found it after an hour searching.
Open a pattern and look to see how much fabric is really needed. I have had patterns say it needs to be a yard of fabric when it comes closer to only a half yard. I also read the whole pattern before hand. I have been able to change it to accommodate my skill set of sewing tricks and cutting. Know what I mean. I like the easy way.
And lastly, make sure you have gathered all of the related items and fabric you need before you start. I hate stopping once I get started because I forgot to buy something. It cuts down on my enjoyment of a project. Happened just three days ago.