Simple tips to improve

1. Never think you know it all. This will be an important tip to push your dps, that extra 5%, top dps or not it does make a difference. Once you assume you know it all you stop researching, you stop trying to improve, you stop fine tuning yourself and when this happens that 5% you may be missing might turn into 10%, 15% and you will have no idea because you don't know where you should be. Just because your top dps or hps in your group does not mean you are the best, different classes, specs, and gear make it difficult sometimes to know who really is better.
2. Don't always believe what you see or hear. Someone may provide you with an insane number for dps or hps for a fight, it might be true or false, either way lots of factors are involved in this. Shorter fights = higher dps, groups who have classes that shield for heals will falsify numbers for non shielding healers. tanks who are off tanks will take less damage then main tanks, and so on.
3. Get an average comparison for bosses. This does not mean use the overall setting on your recount or skada, this means take a record of your dps/hps per boss, boss kill times and the item levels as well as those numbers from others the same class/spec as yourself. You wont always be consistent but you can eventually form a trend and gain an idea of where you are compared to others with similar gear.
4. Just because your top, doesn't mean your the top. This one may be a bit confusing but often i find in all difficulties you will see that person in 2nd place on the meters, 3rd place, even lower sometimes and think they are not as good as that person in 1st, check again, they could have lower gear, improper spec, or both and for what they have they may be doing great, fine tune some things and they might be highest.
5. Don't be scared to ask for and/or take advice. Sometimes people refuse advice, that advice could be from another random player, a friend, guildie, etc. The point is when someone says use this talent not that one or follow this stat priority, or why is this spell your top damage or healing spell. Don't always assume they are being mean, sometimes they are being a troll but sometimes that may be just what you need to tune your skill.
6. Compete! This does not mean every boss link your damage or healing meters, this does not mean show off and be a jerk. This means find someone who does similar dps/hps or damage mitigation as you or sometimes even a little better and say to them, hay wanna have a dps/hps race? When someone knows your competing they tend to try harder, test yourself, this may help motivate you to improve, i personally have 2 people i compete with on a constant basis, and in the past had others however using the tips i give its no longer a competition and i had to find newer challenges. If you find that person you compete with no longer holds up to your numbers or completely slaughters you, find someone else, equal playing field.
7. Don't overwork yourself. The tips i give may seem overwhelming however they are simple, don't be a know it all, look at your meters, other meters and compare, compete and more in my advanced tips to improve section. They can be done in a short amount of time, very quick and if you find yourself spending an hour wondering if one piece of gear is better then another then your trying to hard, look at it, and either try it our and hack up the gold to reforge and gem and hit the target dummy's or think out loud to friends, or even just give it a day or 2, your character will be there tomorrow, go enjoy the game its not a job, but don't hold back respect for yourself and your group when it comes to raid time. Remember the raid isnt there to gear you, they are their to progress and have fun, respect it and work towards being a part of the solution not the problem.