For what it's worth, I'm not a strong mid player. My mechanical skills just aren't too sharp to go up against the best mids in North America. But there are some general stuff that I know that doesn't get reinforced as much, so let's go over them in no particular order of importance.
Blocking correctly is actually very important, especially when you want mid to be gankable on the first wave of creeps. You want to have creeps around the ramp, where the enemy hero has to attack uphill for harass and last hits. Try to retain this as much as possible for your own safety and edge, unless you see a reason not to.
If you are one of those assholes that go mid and camp the rune at minute zero, promptly kill yourself. Please don't think you are doing any service to your team when you luck out a useful rune at rate of 25% and missing out on block.
Push the wave by 1:52 or so and leave lane to camp rune is standard stuff. It's often a good idea to conserve mana until the rune wave because even if you nuke the wave before the rune waves, you have very little use of the space you created for that. And you want to have a good mana when you get a rune, so that you can be potent with it. Some runes are more important than the other, these are 4min, 6min and 8min rune. These are effectively midgame runes that could have a big impact on the game. So try your best to get them.
This has essentially become a standard. Frankly, I'm not a big fan but I cannot dispute its usefulness. As soon as you realize that you missed the rune control, immediately call the courier for fountain refill on your bottle. This allows smaller gap for loss of rune. Generally speaking, without bottlecrowing, you cannot compete with a player who has rune control. This is essential to be on an equal footing, or somewhere close to it.
Caution: Courier snipe
This is already a thing now in any decent level of game. If you start out with tango and three branches, courier is probably delivering bottle by like 1:30 to 2:00. Try not to let it die, often times, your supports don't have the gold to upgrade the courier here unless they have some cs or hero kill. If they start out with like tango, three branches and a mantle, it's between 2:00 and 2:30. But this is riskier since courier can get upgraded if the team is alert and you may have wasted a lot of time trying to achieve this.
5:52, night begins
Around this time, you should be close to lvl6. For most heroes that go mid, first night is very important. A lot of heroes' vision gets reduced by more than 50%, and the first rune is going to spawn in less than ten seconds. By now, the laning phase is sort of over and the player who has an edge in lane should be pretty clear (because he should be getting the rune majority of the time).
If you lost the 6min rune, then you best get a TP scroll immediately, so when their mid ganks somewhere, you can also be there. If you are low on mana, then bring clarity or whatever, just be in shape to help. And no, calling mia is not enough. You know what that is? It's masturbation. It's you rubbing one out in your lane and feeling good about yourself while the others suffer. Don't do that. Try to get involved and help out. Anyway, in the mean time, push the lane and chip the tower and allow the enemy to pay for his absence in lane. After the first night, you want the mid tower dead now, and faster the better.
Generally, from this point on, you want to remain unseen as much as possible. So you can resort to nuking lanes and clearing creepwaves fast, create that space and disappear to look for opportunities. To achieve this effectively, bottlecrowing often to replenish exhausted mana is not a bad idea, just make sure that you are using courier efficiently so that you aren't hurting the team.
If you are on radiant side, you can actually stack the small camp yourself whenever you get a chance. Even if it means you are missing a cs or two, it still nets positive for you. For this reason, some players prefer certain heroes more on radiant side than dire, and could play a factor in drafting.
This doesn't matter too much if you outclass your opponent, but if the two players are close on matchup, this is important. You need to pick a potent mid that at least goes 50:50 against the enemy mid, and be useful as a mid hero for all other purposes. For what it's worth, having an extensive library of matchup knowledge is very powerful because some people just don't know how to react against your hero, especially if it's a hero that doesn't get picked often. It's just another way of acquiring advantage before the game is even played.
If you have decent mechanical skills, employing all of these pointers above should allow you to crush most pub games.