Titans have a lot of advantages over on-foot Pilots, but Pilot are faster. Use that to your advantage.
If you want to get a Rodeo Kill by getting on top of a Titan, ripping off a panel, and shooting it, you should beware of a few things. First, if you try to jump on the Titan from the front, it might crush you. Your best shot is to get on top of it from a higher area, such as the tops of buildings. Second, you will be vulnerable to enemy fire while on top of the Titan. Third, the Titan’s Pilot can leave the cockpit to attack you.
Use the Archer Heavy Rocket as a ranged weapon.
For Titan vs. Titan combat, make use of your Vortex Shield, but also considering alternating attacks between your main weapon and your ordnance. The XO-16 Chaingun, 40 MM Cannon, and Rocket Salvo ordnance are all effective.
If the enemy Titan is almost dead, a melee attack against it will cause you to rip open the cockpit, grab the Pilot, and throw them to the ground. Do this when you can, but do not take damage just because you want to try it.
[more cheats for Titanfall here]