T7 Malz main here. Start with his E first, and get dorans. AD Malz is dead since the rework. Keep in mind his Q now resets his E on targets, so try to hit targets right before your E ends. Your W is trash, but is your highest source of damage, use it on enemies who are locked down by you or somebody else. But otherwise it is unreliable. His W is great for clearing jungle camps and assisting with dragons, always be present for dragons. The clusterfuck of minions also helps protect against skillshot steals.
In laning, play safe, farm and abuse the E mana return. Aim for Morellonomicon first, I get Liandy's second, Rylai's third and then Deathcap. Whatever follows is optional. Always Sorc Treads.
In team fights you should be focused on silencing as many enemies as possible, while getting your E on the lowest health target you can, if they die it will spread, you want that. Only throw out your W once their main AoE burst has been blown, as the minions die easily and the CD is long.
Only R when your positioning is safe but the enemy is not. For instance, if an enemy Zed jumps into your team, and you are safe in the 'core' of your team. You want to put E/W down on him then ult him. But you should not ult anywhere you are not safe or could be crowd controlled. Remember, his ult suppresses himself as well.
Don't engage in fights without you passive up, unless you absolutely MUST with your team. You are much stronger with it up. Keep in mind, even an AA can cancel it though, try to not let them hit you with something benign so it is not wasted. If you want to be derpy, make your last item a Banshee's veil XD.
Most of all, have fun with crabs and aids! GG!