I've covered surviving as a Rogue. It's essential. Live longer and do more damage. But that's just part of what it means to be a Rogue. Our primary role is to deal damage and lots of it. How we (and copycat Druids) do damage relies upon the energy and Combo Points systems. The Combo Points and Finishers system is significant enough to be deserving of a separate discussion, so I'd like to focus upon the energy system and how to maximize your energy regeneration first.
Every tick — 2 seconds — you recover 20 energy up to your maximum, which is normally 100. Like Warrior Rage, your maximum energy doesn't increase as you level, though it may with certain gear or talents. Your energy recovery rate also never changes, but you can regain energy by utilizing Thistle Tea or similar items or through certain talents or gear effects.
Energy equals damage. About 50% of the damage a Rogue does comes from special attacks, attacks which are powered through energy expenditure. This damage is generally called "yellow" damage because it shows up in yellow text in your combat log. Normal auto-attacks generate "white" damage for the same reason. Since all special attacks require energy, any increase in available energy allows a Rogue to use more abilities, and thus generate more damage. One of our abilities, Slice and Dice, increases white damage, as well, making it hard to pin down an exact number. As a general rule, however, our damage output is tied directly to our energy recovery. Basically, you can estimate that an increase of 2% in energy regeneration should result in a 1% increase to overall damage (via special attacks).
The primary ways of regaining energy outside of innate regeneration are Thistle Tea and the talents Relentless Strikes, Adrenaline Rush, and Combat Potency.
Relentless Strikes is the first accessible talent that allows you to regain energy at an accelerated rate. You can and should pick this up at around level 22. For each Combo Point you have when you perform a finishing move, Relentless Strikes gives a 20% chance to regain 25 energy. So when you perform a 5-point finishing move, you have 100% chance to regain 25 energy. It's hard to judge the exact increase from this, but I've had it trigger about 3 times a minute over a 43 minute fight. That's about 12.5% increase to energy/6% increase to damage.
At level 51, if you choose to go Combat, you should pick up Adrenaline Rush. Every 5 minutes, Adrenaline Rush can be used to double your natural energy recovery for 15 seconds. Since we get 20 energy every tick, you get 40 energy for about 7-8 ticks, or an extra 150 energy. That's a 5% boost spread over five minutes. However, it's best to be applied during situations where you are trying to apply a high level of damage in a short amount of time. For this reason, most Rogues pair it with Blade Flurry.
You can technically pick up Combat Potency at level 49, but because you should also have Relentless Strikes from the Assassination tree, you won't be able to pick up Combat Potency until level 60. Combat Potency has a 20% chance for each off-hand hit to generate 3 energy per talent point, or 15 points for the maximum five points you can invest in it. Combat Potency gives me 37% more energy than Relentless Strikes, and I try to use 80% of my finishing moves at 5 combo points which gives me a lot of energy back from Relentless Strikes.
For Rogues with fast off-hand weapons, this adds up fast! I have a 1.5 speed weapon, so I should get about 40 swings in a minute. If 20% of those 40 swings trigger the Combat Potency energy regain effect, I should get 120 (8*15) extra energy back from Combat Potency every minute. That's a 20% increase in energy and, therefore via our estimation, a 10% increase to damage. Weapons with a speed as slow as 2.0 will only give about a 7.5% increase while those with a 1.0 speed would increase damage about almost 15%! Also, any haste or Slice and Dice also affects your weapon speed and should add to the amount of energy you regain through Combat Potency.
In the combat build, energy recovery is an important source of damage. Through Relentless Strikes, Adrenaline Rush and Combat Potency, Combat Rogues can boost their damage 18% by supplementing their normal energy regeneration.