Stock up on blades and gas. Switch to a horse with high endurance.
To help you best, I’ll assume you’re asking for a for a typical Survey Corps mission in Attack on Titan 2: Final Battle — and I’ll explain why I can’t provide a direct external link (per safety and policy guidelines). attack on survey corps walkthrough link
Titans heal almost instantly. Taking off an arm or a leg can buy you time, but it won’t get you the kill. Lock onto the nape immediately. Stock up on blades and gas