Even if you don't memorize the percentages in the chart below, it's very helpful to have a general sense of how common each roll is.
Dice Roll - Probability
2 - 2.78%
3 - 5.56%
4 - 8.33%
5 - 11.11%
6 - 13.89%
7 - 16.67%
8 - 13.89%
9 - 11.11%
10 - 8.33%
11 - 5.56%
12 - 2.78%
As you can see, 7 is the most common roll with 2 six-sided dice.
It's six times more likely that you'll roll a 7 than a 2 or a 12 -- a huge difference. And it's twice as likely that you'll roll a 7 than a 4 or a 10.
However, it's only 1.2 times more likely that you'll roll a 7 than a 6 or an 8.
Another way of looking at these numbers is that, over time, you will roll one 4 or 10 for every two 7s rolled. You'll see six 7s for every 2 or 12.
Of course, dice have a bad habit of defying expectations. Don't rely on probabilities to work out precisely according to a chart like this -- you'll often find yourself on the losing end of a game if you do.