League-of-legends – Experience; Stay in lane or gank

Assuming you are the mid lane, you should gank top and bottom lanes more frequently than if you had a jungler, the following are just general guidelines to bare in mind before/during/after ganking.

Before

• Make sure mid lane is not pushed and that either enemy mid lane pilled back or you killed him.
• Check both side lanes for enemies overextending and being below half health.
• Either ping and type in chat your intention to gank, if possible ask whether the side bushes are warded, this will save you time and lost exp/gold from minion kills.
• Depending on the champion you are playing you will most likely need to be at least 6 to make use of your ultimate.
• Make sure you have your summoner spells not in cooldown, successful ganks can be determined on this, wise use of ignite/exhaust and ghost/flash to catch up will almost guarantee a kill/assist.

To answer one of your questions determining when is early or late, usually mid towers are taken down in 15-20 minutes of gameplay, you should not gank if you are going to loose mid tower as it is the most important tower you have, therefore taking into account the things I mentioned above too early would be not having more than one of the aforementioned; as simple as it is, too late is whenever the side lane towers were taken down and you had the opportunity to gank.

During

• Make sure you and your teammates focus the weakest/most important target.
• Do not tower dive if the gank is most likely to fail, it is not worth to get 1x2.
• Do not ignore minions during the gank, specially if you are below 1/4 health! Beware of the purple caster minion (Specially during early game)!

After

• After a successful gank from mid, you can either push the lane you just ganked in order to get the tower gold and experience, this should be done if you can be aware that a counter gank is not going to happen and also if mid lane is not being pushed.
• If you are not going to push the tower, you should leave the lane for your teammates to farm gold.
• If you ganked bottom lane and if you and your teammates have the appropriate map control you can all get dragon, it gives global gold as taking a tower does, but it is worth more during early/mid game.

At what time do i expect a gank?

Expect a Gank anytime when you see the lane not being pushed and 1 or more of the enemy champions missing in action, expect a Gank whenever the enemy lane becomes over confident being below half health, meaning you are being lured into a trap. Expect a gank when killing enemy Blue/Red and whenever killing Baron and Dragon.
Best Counter gank: Proper warding of the map

From what I've noticed, you get an average of 21 gold per minion, 8 minions per wave.

An average kill is 260 gold and 2 waves is 336 gold (at least this how it was a year ago)

However, more assists/kills you have the more the enemy gains if he kills you so basically a person who's on a killing spree is worth more to kill than 2 waves of minions.

I'd say the new item came from being able to simply go back before you, not that he had more gold than you unless the person he killed was worth a lot.

Melee Minions

• 3 spawn in every wave
• 22 gold during the first wave on Summoner's Rift
• 29 on Twisted Treeline
• increases by 1 after the first wave
• +1 after every 5 minutes game-time passed

Caster Minions

• 3 spawn in every wave
• 16 gold on Summoner's Rift
• 22 on Twisted Treeline
• +1 after the first wave
• +1 after every 5 minutes

Siege Minions

• 1 spawn in every 3 waves (one every 2 waves after 20 minutes game-time)
• 27 gold during the first wave on Summoner's Rift
• 36 gold on Twisted Treeline
• +1 every 2-3 minutes