you have got to think "what can I give". Sponsors wont give you anything for nothing.
Sponsors will give riders stuff (discounts, parts, money) as long as they are getting the promotion to the punters who could be buying the product.
Comp riders will get sponsors if they can get good results and their names on the results sheets. Some sponsors my support riders if they make promotional videos others for doing shows and other promotions.
I am lucky in that I have some great sponsors. I used to do fairly well in comps, but more recently I have (with OBM's help) gotten a good selection of good quality photos and video footage. But I also do shows with the Clan and have just got back from a video and photo shoot with Victoria Penalton (name drop) in London for a Gatorade ad campaign.
If you work hard, get good on a bike, behave well and get people to want what your running then your on the road. don't forget why you ride though, riding to me has and will always be for the fun (and the money if I can get it lol).
Have a search, I wrote a longer "guide" in the past