Taking cash advances and paying it back doesn't build credit any better than just buying gas (for example) and paying it back. You can build up your credit score by getting another credit account and using/paying it. I'm not a banker, but as I understand it having a couple of paid up to current accounts is better than having one higher limit account.
I never had a credit card or any other real traceable credit untill I went to buy a house. It was a tough deal to put together. One thing I learned is that mortgage brokers know quite a bit about how credit really works. Here is somethiong you can do. Go to a mortgage broker, tell him that you want to start thinking about home ownership (maybe not right now, but you want to start thinking ahead about it) but your credit is weak. They will pull your credit report, help you figure out how much of a mortgage they could help you get (usefull info) and *important to you* what you could do in the next twelve months to bring up your 'borrowing power'.
I am a firm believer in asking experts in any given field for advice in that field. When I have a tax question, I go to a CPA. Legal questions? To a lawyer (not a cop). This sort of credit question should go to someone in the business of dealing in credit. A banker (who works in loans, not a teller) a mortgage broker, someone like that is going to be able to give you meaningful, actionable information.
