Five factors govern the formula used to score your creditworthiness:
Your track record as to paying on time: Their objective is to weed out late payers, people who are “a day late and a dollar short”. In particular any payment above 30 day late will affect your credit score. This amounts to about a third of the factors affecting your score.
How much do you owe? Here it is not so much the amount that matters but the proportion of credit that you use compared to what has been extended to you. They dislike people who max out their credit card and look for credit utilization lower than 30%. This factor will amount to another third of the score.
Length or credit history: this will take into account the age of your credit accounts. They will also look at how often you’re using your accounts. So keep your old accounts even if you don’t use them. About 15% of your score will depend on this.
About 10% of the score will depend upon new credit: when a number of new accounts are added, or credit inquiries pop up (“Hard Pulls”), your credit score will be negatively impacted. Just note that this is transitory as after about one year, the impact of these new credit applications disappears.
Finally, another 10% will depend upon the structure of credits received: credit cards, personal loans, mortgages.
Armed with that knowledge, it becomes easier for you to monitor and control how your score evolves.