Play half an hour of quake 1 with a rocket launcher or any weapon really and then play TF2, because of the fast pace of quake 1 TF2 will feel like it's in slow motion.  

There are still a lot of quake 1 servers going, I realized that this works when GB did Quake 1 on TNT, after TNT ended I played a little TF2 and I was killing everyone really easy even scouts which I usually had trouble with. Try it and tell me how it goes :D.

I've read that Solider is the easiest class but it's actually my least played class. I totally suck at it.

Best way to get good at soldier? Switch to demoman. 
 
Lighthearted trolling aside, I find that really getting your quick swapping down helps a ton. Knowing when to switch to shotgun is key. Learning your role is also key. You're there to do long-range damage, particularly to engineer defenses.

I think your advice is sound for any of the classes, it happened to me coming from Quake 3 online and it´s true, although I chose to focus on the scout.

Pro-tip: aim at their legs.

Shoot that floor ...get them kills son

There should be some worthwhile tutorial videos on youtube that you might want to check out. Anyway, aim at their feet for splash damage, jump while firing or use higher ground to spread the damage. Work on rocket jumping, it gives you a significant advantage once you can pull it off reliably. Fire a rocket at your feet while jumping (or crouch jumping) to pull it off, preferably have some momentum beforehand. It not only aids you in killing enemies but it can work quite well defensively when you need to retreat quickly. Rocket jumping also lets you reach areas most other classes couldn't. You can juggle enemies mid-air with your Rocket Launcher too, you can send them in the air with the splash damage at their feet and follow it up with another rocket while they're still in the air.
 
If you get ubered and need to take out an engineer and his sentry, kill the engy first. If you've used all four rockets, switch to the shotgun to finish the job rather than reload the rocket launcher. You can also take down sentries from far away by spamming rockets at it. If a sentry is right around the corner, aim at the ground close to where it is and finish it off with splash damage. 
 
It's fairly easy to become competent at soldier but being able to do more than shoot the floor separates you from the pack.

Would love to help but TF2 is broke makeing me fucking mad each time i try to start it loads up the valve intro and then crashes have tried to delete the local files restart steam restart my pc scan my entire for virus on 4 diffrent programs and its still fucking broke its fucking bullshit i was playing just 2 days ago and now its fucking broke and there is no way to fix it!!!!

I've read that Solider is the easiest class but it's actually my least played class. I totally suck at it.

I just use the Direct Hit. I'm not a fan of the disappointment that is splash damage.
 
@valrog said:

Easy to grasp, difficult to conquer. Soldier is my second most played class (Right after Sniper) and I'm still learning new things every day.

I think this video will help you a lot

Shoot at the ground.