1. Try to anticipate where the enemy will be in three seconds, when your TNT blows up. If they're moving towards you aggressively, place a TNT behind them.
2. Pistols, if you practice with them a lot, can really boost your K/D and your points.
3. JUMP AROUND! too many players don't, and you can avoid many weapons this way.
4. Move around sporadically, and try to be unexpected. When you do this, it is easier to dodge enemies' TNT and other weapons.
5. Get a strategic position (like one block above your enemy) for your shooting weapons to be more effective.
6. Try to save up for the upgrades. Many of them are worth the cost.
7. Try to explore new weapons. I used to play with just shotgun and TNT, which made it very difficult to save up points, as shotguns usually cost more than the reward for killing. Now, I have started using pistols, rockets, cannons, and other weapons that are most effective in certain situations. I have more points than ever before :D