Mid as a role is extremely versatile and next to jungle perhaps the most crucial role in the game.
Your goal as a mid player is to get ahead of the enemy mid laner as soon as possible, for a number of reasons. When you get ahead you can decide whether to pressure the mid tower (the most important outer tower early in the game) so as to draw in the enemy jungler and grab his attention so he can't influence other lanes. You can decide to perhaps roam bot and be a constant thorn in the side of the enemy adc and his support, thus once again drawing the attention of the enemy jungler and forcing their duo to play very defensively and not be able to guard drake that easily. Alternatively, if the enemy has a snowball carry jungler (Nida is a great example of a snowbally carry jungler that is utter shit once set far enough behind) you could help your jungler bully their jungler thus robbing him of his strengths and putting your own jungler ahead so he can project the lead onto the outer two lanes. The reason I'm mentioning helping top last is because in the current meta, helping top is by far the shittiest option no matter how you look at it. Most of the time top is going to be tanks, and tanks give zero fucks about being behind - they can easily do their job even with 60 less cs and being 0-10.
That's why mid is not for those who don't know what to do when ahead and don't think in advance. It's the lane that has the potential to influence every other lane (and jungle) and make the enemy feel even the smallest of the gold lead set by your mid laner.
Study matchups and your own teammates (some people are not worth assisting for shit - like easily tilted ones), learn when to roam to top, when to roam and contest drag, when to push/pressure and when to just farm.