What are the two most important factors in calculating your credit score?

Different scoring models weigh the importance of factors differently. The most common scoring models are FICO® and VantageScore®. With the FICO score, payment history and amounts owed make up most of your credit score:
Payment history makes up 35% of your FICO score. Lenders look at whether and how often you have paid your past credit accounts on time.
Amounts owed make up 30% of your credit score. Lenders also look at how much of your available credit (this is the sum of the credit available on all your credit cards: your total revolving credit) you are using. Your credit utilization ratio needs to be less than 30% for a positive impact on your credit score.

This is how VantageScore weighs its factors:
Total credit usage, balance, and available credit are scored as extremely influential factors. This means that your credit utilization ratio has to be as low as possible for a good VantageScore. This ensures a low credit usage and balance, with high available credit.
Credit mix and experience are other highly influential factors in your VantageScore. The older your credit history, the better your chances of approval by lenders. Moreover, if you have a diverse credit mix: credit cards, auto loans, mortgage loans, and education loans, your credit score will be higher as well.