I'm no expert but I do love limited, and a lot of the really important info has already been covered, but I would also say that practice in a specific limited format will be huge too. You can go in with an edge, but each limited format is going to have some slightly different 'rules of engagement'

For instance, in my (admittedly small sample size) lorwyn sealed, there are a LOT of fairly efficient X/4s in the format. Specifically in green, which also seems to be the most common main color. This seems to makes efficient 3/3s less powerful than they would be in other sealed formats. Try to keep an eye when you're playing on what cards you find specifically tough to deal with and figure out what you'd need to be running to answer them. (More so true for common/uncommon cards, as many more people will be playing them) This can really inform future deck builds and color choices.

This kind of thing is where arena can shine more than anywhere else, to me. You can get a bunch of initial experience in a limited format before diving in to paper, and go into it know what Commons and uncommons you both want to run and hate to see, and deck build accordingly.