I really wish there were great things to explain, complex strategies and all that, but the truth is, you just need to do the basics.

See, at the beginning of the game help your jungler (if you need to) and simply use Q after Q poking the enemy botlane.

Use your cookies when you're at half mana, as your job is to spam your Q until you reach Lv6

At Lv6 all you need to do (apart from spreading your space aids and silencing everyone) is focus on priority targets.
always the most troublesome guy on the enemy team in the current situation will be your target.
Example: the enemy jungler approaching while your team is trying to kill the dragon, it doesn't matter the rest of the enemy team, you need to ult the enemy jungler, he is the priority target in the current situation.

Other than that, you just need to do basic support, give your team vision with wards, avoid face check with your Q (which gives vision in the first instance), roam from bot to mid and from mid to top, etc.

But most importantly, be annoying
like, really ****ing annoying
don't let your enemies breathe, don't let them catch you, dodge as many abilities as possible.
because they're going to focus on you, you can be the support but you're still a Malzahar