In CTF, NEVER park your warthog outside of the base like 30 meters from the inside. Running to it is very risky and by the time you get to your hog or ghost, they'll probably throw a nade or two and easily kill you.
So, what you should do is the quick grab. What you do is drive through their base and quickly jump out and enter in a second or two. This way, you won't have to start it completely and you'll still have some speed. That way, you can avoid having to run to a vehicle and get naded to death.
Note: This only applies to Sidewinder, Timberland, Death Island, Danger Canyon, and Infinity.