I am an avid user of credit karma and swear by it. With that being said don't quote me but this has helped me boost my score north of 140 points. The major factors that affect your score (according to credit karma) are:
1. Delinquencies - Always pay everything on time. Setup automatic minimum payments and pay extra to your highest interest bearing account. Pull recent reports and dispute discrepancies and try to settle accounts in bad standing.
2. Bankruptcies - If you have a bankruptcy on record this will be the hardest impact on your credit score. It takes time and doing well in all other categories to overcome this.
3. Credit Card utilization - Excellent is using below 10% of your total limit on all credit cards. Great is 10-20%. Good is 20-30%. There is a drastic drop in points once you pass 30% utilization of credit cards.
4. Hard Inquiries - Hard inquiries are anytime credit is applied for and an SSN and authorization is necessary. A hard inquiry remains on your credit report for 2 years from the date you applied then is removed. Excellent is less than 1, Great is 2-3, Good is 3-4, then steeper drops in points when you have 5 or more hard inquiries in a span of 2 years. If you shop around for mortgage or auto loans within a 2 week time frame, the credit agencies consider these as one inquiry and shouldn't negatively impact you for shopping around.
5. Number of accounts - Each open loan, closed loan, and open credit card counts as an account. The more accounts one has then the more responsible that individual is with credit. Excellent is 21+ types of accounts, Great is 11-21, Good is 8-11.
6. Age of accounts - This metric takes the average age for all of your accounts. If you have one account opened 10 years ago then your avg is 10 years. If you opened 3 new accounts in addition to the 10 yr account then your avg age will be 3.3 years. Excellent in this category is 10+ years, Great is 8-10 yrs, and Good is 6-8 yrs.
2 things to take away from this are this:
1. Figure out how many inquiries you have on your report and figure when they will fall off the report. Time this with being able to apply for new accounts (responsibly of course), not going over 4 per 2 years, so that you can increase the number of accounts and start building the age of accounts.
2. Find out how to decrease credit card utilization. If that means applying for an unsecured loan to pay down CC debt and pay fixed payments then that could certainly help in that sense.
These ideals have helped me drastically and I learned all of it from Credit Karma. By any means do not solely take my advice as I am not a professional in these fields.
Good Luck