The Overwatch open beta starts this week. Early access is May 2 if you pre-ordered, and it fully opens up a couple of days later.
Overwatch is an amazingly fun game, and I'm a terrible FPS player. I wasn't in Closed Beta, but I was in the stress tests. So here are some tips from someone who is probably worse than you are.
1. Don't be afraid to solo queue.
Obviously, if you have friends, queue with them. But the solo queue is surprisingly balanced. It seems to quickly find your skill level. As well, matches aren't independent of each other. The players from the last match will be the same players in the next match. Only the teams are shuffled. So maybe there was an awesome enemy Pharah last game that kept killing you. This game, you might end up on the same team as her. This goes a long way to keeping the matches even and popping quickly.
2. Don't bother with AI games.
Maybe play one match to get the hang of things, but I would recommend jumping directly into matches with other players. Playing against the AI just isn't the same as playing against humans. If you want to figure out a hero's abilities, use the training room to see how they work, but then fling yourself against other players.
3. Try to focus on one hero from each category.
There are four categories of heroes: Offensive, Defensive, Tanks, and Support. You generally want a mixed squad, so if you're capable of playing at least one hero of each type, you can fill in for any missing element. Also, tanks and support can be a little more newbie-friendly as they are less reliant on aim and are often a little less fragile than the others.
4. Don't switch heroes too much.
You can switch heroes every time you die, but I recommend playing the entire match as the same hero, at least at the start. They do take some time to get used to, so they might feel frustrating at first until they click for you.
5. Stick with your team.
If you're all alone, it's better to retreat for a few seconds and meet up with the rest of your team, rather than throwing yourself at the enemy. Also remember that the game is about objectives, not a death-match, so emphasize pushing the objective.
6. Use ultimates aggressively.
Ultimate abilities charge quite quickly, so don't hesitate on using them. You have to fail with them a few times to figure out how to use them best.
7. The Kill Cam is your best teacher.
Whenever you die (and you will die a lot) a kill cam will come up showing your death from the opponent's point of view. This is the best way to learn. You can see what you did wrong, and see what your opponent did right.
I think Overwatch is an amazing game, and I strongly recommend that you all try it out. There are lots of different heroes with different playstyles, so I'm sure you'll find at least a couple you enjoy.