Managing your project - meet your Requirements First
Don't stray from the original requirements to do work that is sexier, or is the result of scope creep. I've seen this time and time again. Especially with those new to freelancing. This is not a problem limited to freelancers though.
Complete the initial task first. Before you run out of time and money. Then go back and add the polish. At least when you finish, you'll have a usable product ripe for an up-sell.