Building good credit is not something you can do in 1 year. I got married at 18 and our 1st credit card was a Sears card. The only way we got that was by having a co-signer. Over time you just need to open accounts, use them, and make sure you pay them ON TIME. On your credit report you can get reported for being 30, 60, and 90 days delinquent. All of those will hurt your scores.
There is no secret way to do it, but it takes time. Ive now been married 20 years this Sept and we have more credit being thrown at us than I want. The best part is now instead of begging them for credit, I call them and tell them to lower their rates or ill cancel my account with them.
Getting and keeping good credit means that you are the one in the position to bargain. They know they need to compete to get your business, or you can just tell them to get lost and move on to the next financial institution.
Good luck