He's a really good duelist. Try to keep your heat at/around 50% at all times. This will empower your abilities yet still allow you to cast them. So he's a steady spam champion. Don't abuse flamethrower too much, it will shove the minion wave. If you plan on overheating cast abilities in following order: Shield, Flamethrower, harpoon. You will now be heated, your shield is most likely gone (nobody ever maxes it anyway), your flamethrower is active and you have 1 harpoon to use as you see fit in the next 3ish seconds. And when overheated your auto attacks are empowered. Rumble thrives on burst style team compositions. While he isn't a bursty guy himself (he is damage over time) his passive gives him an exploitable window to be ganged up on. Right when he is overheated and his flamethrower and harpoons are on cool down and the next 10 seconds it takes for him to get back to 50% heat. Roughly 15 seconds. A burst comp usually kills a target completely making Rumble's window of weakness unable to be exploited upon. So if your teammate picks an assassin jungler (Rengar, Kha'zix, Fiddledix, Evelynn, etc.) Rumble is a prime pick.
Alistar is ok. He's a sleeper pick along with Taric because tanks are strong right now. Everything Akeydel said is true. Act like a tank, troll heal and learn the W+Q combo. There are reach arounds to that W+Q combo though. You can actually headbutt a minion as a gap closer and then hopefully you are close enough to Q them into the air. Your ultimate is great for tower sieges, both defense and offensive sides. His ultimate removes any CC (except silences) that are currently affecting him. So Alistar can safely jump in the way of an Ashe arrow, take the stun and then ult it away as if nothing ever happened. He will not be stunned or slowed if timed properly. When your ultimate is active do not be afraid to take more damage. Even tower shots. Its got an 80% damage reduction. Abuse that. As far as laning phase goes Alistar is pretty good at playing the defense side. He deters jungle ganks by being able to headbutt any would be attackers off his AD and his knockup is extremely disruptive too. He can heal moderate amounts of harassment damage with his heals and can also troll the enemy ADC's last hitting attempts. And since he is a support he will be buying wards. One trick I like to use as an escape tactic is to ward right where the gromp is and headbutt the gromp to get around the wall. Works on any camp but that's the one I like doing it on the most.
One of the few champs I don't own. Can't really give you any concise tips though just stuff I have seen. You can use lunge to cover ground when chasing, it can also be used to dance around an enemy (kinda like Yasuo does) and just overall be annoying. Your reposte thing works on some champions ability casts but I am unsure as to a majority of the ones that do and don't work on it. Ezreal's Q gets reflected back. Riven's Q does not (but the auto attacks do). Jax is the number one guy you want to pick Fiora into. She can reflect back Jax's empowered hits and her ult is a work around Jax's dodge spin ability. And one last thing, the target you ulted on is the same target you will land on once the ult is over. The only exception is if said target died in the process. Enemies who know this will exploit this. Watch out for Blitzcrank grabs and Thresh hooks upon exiting an ultimate.