Set up minions so they can crash into your tower. In other words, make sure casters are at full health and melees are at a little more than half or full horizontally.
Your minion wave doesn't have to be pushed. It is perfectly fine even for their wave to hit your tower. However, you generally want to freeze the wave for the early game until you can roam or if you you get a kill. In either case use abilities to clear minion waves, making sure to crash it to their towers.
Also, your Q can be used in two ways. Trade with it when you get harassed for walking up to CS, always throw after killing the minion so it hits only the other laner. You can also use it to finish off the creep. Sometimes you may be able to align it with the other player for some additional damage. It depends a lot on the match up. Use the first option if the enemy is staying closer to the casters and the second option when they are closer to melees as a basic Idea.
WEQ combo is also amazing for trading against an enemy harassing you.
Also prioritize dodging and trading when they are on CD.
Refillable pots are also extremely useful for laning against poke heavy champions.
Wave management in general is also very big in mid lane. You will lose lots of CS, exp, and possibly tower by roaming at the wrong time. Make sure you are crashing a wave in to their tower before you roam, don't just follow their roam either. Sometimes it better to stay and CS. If the other lane doesn't consider your pings, there is not much else to do. I would recommend you watch LL Stylish's laning phase and how he roams and plays certain match ups.
This is just the tip of the iceberg sadly.
As for teamfighting, there is a lot to consider. For starters, know the combo you want to use and how you plan to execute it before you go in. For example, say I want to outplay from low hp in the jungle. Before I do anything, I come up with my plan. For this instance, you have the ability to w over a wall, ult the squishy, take your w, e, triple q, ult back, aa, ignite, the squishy. Now, you start to do your plan and adapt for any contingencies. Perhaps one of their teammates comes to them. Instead of taking your ult back, you may have to give up on the kill and run away, perhaps blowing flash in the process. Things happen. Be prepared to adapt.
Secondly, keep their team comp in mind. There are some major abilities you have to keep in mind, any stun, snare, etc. By waiting for these abilities you can start to worry about just eliminating the enemy team. Also keep in mind your ult is very useful for helping you dodge stuns.
Additionally, prioritize killable targets. I.e. you have a 6/0 Darius and and 4/1 ezreal on the enemy team. I would never ult the Darius because I can't kill him, the Ezreal is a compl at telly different story though.