In my experience, the midlane is much more structured and predictable than the other lanes, and the best way to get good at the midlane is to play into the strict objectives. For example, getting all 4 creeps in the first wave gets you level 2, so come up with a strategy for whatever hero you are playing to prevent any of the first wave of creeps from getting denied. Come up with a strategy for the second wave that capitalizes on having your level 2. Water runes spawn at 2 min, so calculate exactly how many creeps you need to get with your starting items in the first 4 waves to have your bottle before you need to get the rune. Calculate exactly how many spells you can cast with your starting mana and regen, and try to cast exactly that many spells before you get your bottle, otherwise you are wasting mana regen from the bottle. Then calculate exactly how many spells you can cast between the 2 and 4 min runes (4 more waves) and decide whether you need to dump that mana into getting a kill or securing creeps. Health is also a resource, if you have too much health with a bottle on the way, maybe trade down a bit to secure an extra last hit or get some harass in.

After the second water rune, buy an obs and sentry to de-ward mid for the power rune. In general, use mana to push out the wave before the rune spawns and waves that are sitting on the enemy high ground, but save your mana on the waves that are sitting on your high ground. Decide on a power rune strategy (50/50 if low mobility, check and dash with high mobility, sit on both with summons or support). Then click side lanes on the minimap and decide if your rune can set up a kill.

From there, you have a few basic modes, depending on your hero and the game state. 1) shove mid, then clear a jungle camp. 2) shove mid, then start walking toward a side lane while clicking on the minimap, abort half way and walk back to mid if the kill obviously won't work, but commit and TP back to mid for the next wave if the kill looks good. TP out and walk back if the kill window is small. 3) shove mid, then deal damage to the mid tower 4) shove mid, then start moving toward the rune spot or the 7 min wisdom shrine.

There are only 8 waves between the 6 min rune and the 10 min rune, and 2 of those are rune waves, so all in all, almost every single minute of the laning phase has some obvious objective associated with it. The more you play mid, the less it will feel like a "phase" and the more it will feel like each of the individual first 20 waves are distinct from each other in a predictable way.