This isn't much of a hint as it is just fun. If your trying to beat the game,don't attemp these. If your just are playing around, try these. You can smash your opponent with the trunk part of your car (ONLY your car) by boosting a long way and right where your enemy is, you slide into them. This is extremely difficult, and requires a lot of practice. (I RECCOMMEND practicing on the roaming drones in the suburbs level) Another cool thing is to launch your car at an enemy. You just boost and ram right into them. I use this on the drones that flame you as JAZZ in the UNFRIENDLY SKIES mission, since he is smaller and can get under the fire. I tried this on barricade once as bumblebee, when he flails and he clobbered me. This works exceptionally well on shockwave when he is a tank. This technique is pretty difficult at first, but if you keep at it, you'll take away health from and knock your opponent off guard. You can also shoot down blackout in the UNFRIENDLY SKIES mission. It made it much easier to beat that level. Experiment with different levels, missions, and enemies to figure out how these tricks will work. I'll try and keep you posted about new techniques, because it makes you look cool and the enemy look foolish and weak. I still can't find all the energon cubes but I'm 97% done with the game. Can anybody tell me what the 7th movie is about? I might be able to find all the cubes, but it's hard. See ya
Hint#1, Bumblebee: When you are fighting Barricade as Bumblebee, throw a car or a bus at him to stop his arms spinning. After that, run straight at him, firing your strongest weapon. When you get close, melee him (using the  button) until he is down. Then, when his arms start spinning again, repeat.
Eventually, he will flee to another location. You must get to each location before he does. Then repeat until he is dead.
Hint#2, All the Autobots: This isn't actually a hint but, it's something fun to do. *WARNING: It is only fun if you like the Decepticons but are playing as the Autobots.*
Since Prime is the strongest Autobot in the game, then you should do it with him. You can do it with other Autobots, but I prefer Prime. Just get out your weapons and shoot everything in sight. And, if you have an excellent imagination, you can speak to yourself and pretend it's the voices of the cops and the army. Basicly, you just wreak havoc on the city.
Hint#3, Ironhide: When you are Ironhide and your not doing a mission, transform and drive around the city. Or you could do the same as Hint#2.