How do you make your weopons in Fallout New Vegas have better condition?

Answer 1

You can repair them by combining them with another one of the same weapon. The exact amount added to the original's condition is determined by your repair skill.

When you look at the weapon in your inventory, you can press R to repair/maintain it (repair is for when the weapon's condition is low enough to affect the stats, maintain is for while it's still above that threshold) as long as you've got another of the same weapon.