Most games you can score the most points by destroying the maximum number of bases permitted. However once you've completed that task there are a few techniques available to generate big points:
1 - Tag players where you score the most points, for Nexus that is the chest and the back
2 - Don't hang around with too many of your team mates, if you are tagged all together the opposing teams will be scoring well and you'll need more points to rise to the top.
3 - Defend your base well, as the game progresses and more players are trying to destroy your base players will be coming to you rather than you having to move around to hunt them down
4 - Find a great spot to hide with plenty of arena field to tag.
5 - Move around don't sit in one spot too long, the more you move, the more players you will find.
6 - Blast away - most games are unlimited so you don't ever need to hold back unless you are trying to be sneaky
7 - The penalty for being tagged is far less than the benefit of tagging someone, be on the offensive and don't sweat getting tagged once in a while.