Here we go over a few basics before going over specific mid heroes. I know there are other guides out there and I'm sure they're great and much better than mine; still I would like to cover this in order to have some semblance of a foundation.
1. Blocking
You block in order to have a favorable lane position. I don't know what other people consider the perfect block/position. I like to have it right on top of my ramp. Your opponent is going uphill and does not have vision of you.
If you find yourself in the unfavorable position you can right click an enemy hero (your opponent or any other hero on the map) to draw creep aggro and then click somewhere else to remove aggro. This will flip the creeps around so you can CS better. Also do this when you are a melee hero or in any unfavorable match-up, but note that it will push the lane.
Due to the wave being on your ramp, the lane will push forward during the next wave. Because of this, some players like to let the ranged creep go first in the initial block. I do not recommend doing so. You will most likely not have the first wave positional advantage and without a ranged creep a large combined wave will push into your tower. However, if you let the ranged creep go at the last moment, only the enemy ranged creep will attack your ranged creep and not the melee ones. This is often a very useful way to block.
To maintain favorable lane conditions, it is advisable to go back and block new creep waves as situations permit. E.g., if you are done creeping the enemy wave and yours is pushing, or if you are losing the lane or fear a gank, or if the current wave is not finished but the new one is arriving you can go back and block a little so the wave will push towards you a bit.
So much for blocking.
2. Rune Control and Bottle Crowing
In general, I prefer not to control runes until the higher levels when I can clear a wave quickly. I may quickly grab a top rune but am loathe to run all the way to the bottom river. Runes to me (and often ganking) are for the loser of the lane (think pudge) or supports. It's better to dominate the lane and eat all the experience and gold. In the early minutes, the crow is mostly mid's and I use it non-stop, leaving the 3rd charge so the crow's speed is not affected. I also usually only need 2 charges anyway because, again, I am crowing non-stop in the early part of the game.
3. Starting Items
In general, you start with enough regen. to sustain yourself until bottle and pad yourself with stats items that you plan to upgrade.
If you plan to rush bottle, a set of tangoes and 3 branches is the norm. With a few CS, you will have your bottle in time for the 2 minute rune (not that you should want it unless it spawns top). Most non-intelligence heroes start this way, as a rule of thumb.
As an illustration we can look at Queen of Pain. The standard starting items are tango, pot, mantle, 3 branches. The branches and mantle will later be upgraded.
With QoP, we are not going to be able to clear waves at the early levels, and we have a lot of lane dominance staying in lane for development. This is why we prefer stats padding over bottle rushing.
In the past year, it has become not uncommon to see QoPs start with tango, pot, CIRCLET, and 3 branches. This I do not advise. The benefits of strength and agility in lane are not worth the relative cost (compared to tangoes for regeneration or branches for damage) and a delayed bottle. For intelligence heroes, the benefits of extra intelligence are more worthwhile. Still, it is often not a bad idea to buy a 4th branch or just leave the 6th slot empty instead (as I do when I play Invoker).
Now, depending on the matchup we can modify our starting items. If we are playing QoP vs. Beastmaster, perhaps we could be greedier and forgo a pot to get our bottle sooner. If we are playing Invoker vs Shadow Fiend, we anticipate a straight CS game in the early levels and start Tango, Claws of Attack, Branch. As a fire Invoker against a QoP we probably wouldn't get away with that though.
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