This is an overview of ways to find more DPS for your character that should be generally applicable. There are many guides and builds published for specific classes that outline the exact powers to use and specific formulas for each. This is not that. The aim is to give you an overview of what to check for on your character to balance stats and increase DPS.
The biggest jump to DPS for end game players actually isn't in the hands of the DPS player at all. These come from having a coordinated team, with buffs, and to a lesser extent debuffs that focus on the DPS. Many of these are multiplicative and stacking when done right, and complement every bit of work that the dps character can get.
This team dynamic is enough for a separate post. Lets instead focus on what you can do as a main DPS to play your part in this team.
As a dps you want to get your armor penetration to the needed level as priority 1. For most of the game this is 60% for chult/omu and related content this rises to 85%. Peg the needle exactly there. Any more is wasted and does nothing for you, and less and you're burning off your other stats work.
Critical strike you want pegged at 100% in the team you travel with. Some classes and companions will add to your critical strike, so be aware of what effects are in use. Anything over 100% critical strike is wasted. If you have a choice of going over 100% and adding somewhere else, add somewhere else. Chances are a team mate can buff you that extra bit and you get the best of both worlds.
Power.. more = better. Power from your personal stats however pales in comparison to what you get from a good team. So put this behind the other stats already listed.
Recovery.. This varies per class. Some like CW essentially don't need it at all, as they speed their spell time up using feats to a point faster then they can cast. Even other classes may not need it in a good group using recovery time cutting powers and when personally using the Shepherd's Devotion mount bonus. If you have encounters sitting idle, thats wasted DPS. You want a nice steady stream of powerful hits.
The main drivers of DPS that you have control over on your character are weapon set and bonded companions. Right now mod 13 weapons, all 4 sets are the weapons to have, no option. For each set the 'damage' stat far outweighs the others in terms of effect on DPS. Each time new weapon sets have come out lately they have vastly eclipsed those that came before.
As of mod 13 you want to have one of: Stronghold 3, Tyrant, Primal, Pilgrim, or Pioneer.
Their stats are all the same, just the set bonus varies. Choose whichever one you feel is best for your class, and that you can manage the grind for. The set bonus is really a minor consideration compared to just getting into the right generation of weapons. Get them to at least purple (epic) level to open up the 2nd enchantment slot.
A good DPS has a bonded pet, no other options. End Game ToNG groups will expect main DPS to have at least rank 13 bondings. Work on raising them to 14 with your ToNG winnings ASAP. Put your best EQ and enchantments on your bonded pet. That way you multiply the stats you get from them.
The summoned pets active bonus should ideally be helpful for more DPS, but thats not as important as having one that you can outfit well. Choose a pet with 3 offensive slots, this narrows the field quite a bit. Right now with the rings that are available, choose one with 2-3 rings slots for EQ. Fill those slots with double offensive slot rings. Fill those rings slots with the highest enchants that you can afford.
These are hard to pin down, change often, and use or avoid powers that may be broken. It is necessary to study your class and what the current information is from people that do testing in depth on these things.
Tooltips lie! Building your character based on the tooltips will get you a playable but not top performing character. They just don't explain what the power actually does, or sometimes actively mislead. So seek out a current guide for your class that will help you learn what each power/feat does, and why it should be used.
We also get 4 other pets that are 'active' but not summoned. Their Active bonus can be quite helpful, and each of the 4 should have some reason for being there. You want active bonuses that have a direct % damage increase of some type. There are a variety of other bonuses available, but those are the ones you want.
You want at least 1 (or more if you can afford it) of your pets to be legendary (orange). The increase in stats is worthwhile, but only after accomplishing the above.
Now we move into areas that won't affect you quite as much per item, but still make up a good amount.
Here again each mod generation can tend to change these out fairly often, and there is often a clear BIS for many slots with a few others that have tradeoffs you may enjoy. These really set the base of your stats like power/crit/armor pen that you can then adjust through the other areas.
Right now Primal in mod 13 is some of the best. Its also upgradeable through restoration if you do enough of the Cradle of the Death God trial. MW3 armor is also worth considering, but the materials and cost of production are so expensive to get, that these are often very pricey.
Relic EQ from mod 10 is now readily available, and much more easily restored for use than it was when it came out. However this is only good for new level 70s as they work on achieving the superior EQ thats available.
Some classes will like some of the dropped pieces in OMU, or even Soshenstar River from mod 12. Many good rings are available that are only now able to dethrone the mighty rising rings from the underdark campaign of mod 7. Even a few of the items from a guild Mysterious Merchant may be of interest for some classes and builds at least until primals can be achieved.
A good mount bonus from an epic mount can be a good supplement. You get 2000 added to the stat of your choice. Legendary of course is better, but the cost of 5-20 million AD often isn't an efficient way to add another 2000 (total 4k) of a stat. The Combat Power that you get from legendary mounts can be an excellent addition, but again the mounts with useful powers are quite expensive, and this is more frosting on the cake.
You get to have 5 mounts in your 'stable', that can add to your stats. Other mounts you own go in an inactive stable where they are stored but do not effect you.
Here you want to have all 5 slots filled with blue mounts or better. This gets you the maximum number of insignias, which allows you to add the most stats possible. These can be great for balancing your stats, with 15 positions each giving you 100-200 for 2 stats each a lot of adjustment can be done here for critical strike, HP, and most importantly armor penetration. A decent DPS will have all these slots filled with at LEAST blue level insignias. They are cheap on the AH. Purple level are nice, but some types are massively expensive.
These insignias are used in different combinations to activate mount bonuses, covered next.
The good mount bonuses most often don't give you DPS directly. They can be great support options however. The mount bonuses that do damage over time eventually will get eclipsed by the other options in higher end groups.
Fairly pricey for what they do at 100k per 200 stat points. However they can be good for making that final tweak to get something like armor pen exactly where you need it. Power kits are not really worth the cost. When boosted by support classes to 200k+ power those 200 +/- aren't going to amount to much.
Campaign boons built up to being a nice set of stats and now item levels. Take some time to do campaigns over time. This is another source of stats that can be used to balance your stats when you achieve a new set of eq as long as you have reroll tokens at your disposal.
Last here, but certainly not least. Guild boons can give you up to 8000 of the crucial stats like critical strike, power, or armor pen. Their strength depends on the level of structures your guild has achieved. This is a massive benefit, especially at lower item levels. There are guilds of every variety so eventually you should be able to find one that suits your tastes/needs. So get thee into a guild!