After two years of really working, scrimping and saving I've managed to get myself debt free... (with the exception of a small student loan) and it's such a relief... but because of my lack of knowledge and irresponsibility in the past my credit score has suffered tremendously... I know it won't happen overnight but what can I do to really improve my score?

I am not an expert but when I was shopping for a mortgage I was given these tips:

Get a major credit card (Visa, MC, Amex, Discover) use it a little and pay it off every month. I use one to pay a bill that I would pay from my checking and instead of paying my cable bill I pay my MC bill.

Buy a car and finance it. This gives you active credit.

Review your credit report for any inaccuracies and challenge them if they don't seem right. The difference between 90 days late and 60 days doesn't seem like much, but every little bit helps.

Otherwise, be patient. If you are debt free, work hard to stay that way.

Well if you are debt free and don't plan on getting in debt does it really matter, The best people I know always pay cash and don't even have credit at all, so basically no score.