Okay so, this is probably slightly more advanced stuff that isn't as obvious. But still pretty simple shit if you take a second to think about it. Remember, ideally, you want to win three lanes. But realistically, you want to try and win two lanes, and neutralize the other. A good execution of pulls will help you win the lane, and this is a required knowledge for being a good 4 and 5 player. I'm not going to bother with various techniques and spots for pulling, you can experiment on your own with that (and there are enough resources out there for that).
Double stack vs. Single stack
What's not good is pulling for sake of pulling. Basically, you are pulling but you don't really know why. You just know you are capable so you do it. This is not good. A pull must have a purpose.
A double stack pull allows you to wipe out that creepwave, denying it from enemy and allowing you to collect extra gold and xp. This is done to control the lane. You want to do this when there's a chance of the creepwave reaching their tower. You don't want the creepwave to reach their tower unless you want it to. And remember, you have full control of this. So there's no excuse for letting that happen. Sometimes you don't have a double stack ready because you were establishing lane presence and you are required to exhaust a creep wave somehow. In this case, you pull and link it to another camp to control the lane. It's harder to do, but this is something you'll have to learn to execute correctly.
Single stack pull is great for pushing. And you want to do this every time you want to put pressure on their tower. It basically stacks your creep wave allowing your side to have creep momentum. Don't casually single stack pull without the purpose of pushing. It is not good.
There are exceptions however. If you managed to single stack pull a hard camp, they are usually strong enough to clear out a creepwave themselves. So, top side dire can take advantage of this for either faction.
When to pull
Well, we already know that you want to pull to control the lane or to push. But sometimes, you are not given a chance to pull. Basically, you want to pull when your lane presence is not required. This may be little abstract, so let's draw some examples.
You have established lane dominance, and you also have a lane ward. Through lane ward, you gain the information that enemy hero is scared of approaching creep wave in fear of death, and has resorted to hugging tower exclusively, waiting for creep wave to reach his tower. You now have room to pull for control purpose.
The creepwave is marching towards their tower, and you have no way to pressure the enemy under his tower. You should have the judgment to know what is needed and should be in position to pull for control purpose.
While laning as top Dire, the enemy Darkseer has ion shelled a creep and sneaked out of the lane to go clear Radiant jungle. You can now go single stack pull and pressure their tower, make Darkseer pay for his absence in lane.
You are a defensive trilane against a suicide (3v1). Only one of the supports will be needed for lane presence to deter the enemy hero from coming near a creep wave. Thus, the other support's lane presence is not required and he is free to pull. During this time, the farmer of the lane should choose to accelerate his creep momentum by actively auto-attacking to create room for absence of lane, so that the enemy creep wave does not march right into tower which makes it difficult for him to last hit (unless he has a quelling blade, at which point he doesn't really care anymore).
But how can getting extra gold and experience be bad over establishing lane presence?
Your net gain is higher if you deter the enemy hero from gaining experience (whereas, you'll be getting experience because you'll be near a creep wave more than he is). Remember, he's there to neutralize the lane. Meaning, he's there to just collect xp and get whatever gold he can without dying. If he manages to do this, then he has successfully neutralized the lane. He basically won the lane. Besides, if the lane is played correctly correctly, you will most likely have room to pull for that extra gold and experience. So it's a double whammy.
If you are in a pretty good level of a game, the concept discussed in this article is very important. Misplaying one pull could really make a difference in a lane. You won't have a lot of opportunities to pull unless your team is super defensive control team where you are still in a laning phase at 10min. Usually, you'll pull maybe 2-3 times in a lane and then you are moving around. So each pull is very important and it has to be executed well.