If you’ve never played a game then that might not be so cut and dry, but I find most of us have a general preference. Once you have found some Warhammer 40K armies you like the looks of, start refining the process by looking at those that seem to fit your play style.
Definitely start by looking at armies you think are visually appealing. I’ve always been a sucker for the big dumb brutes of a game.Ĥ0K Is not a skirmish game, so you will be putting together a lot of models and doing a lot of painting.