The best way to get points in Re5 is to play a chapter and play it well. I would find a nice section to grind in and get it down so you know it like the back of your hand, and then speed through it, the idea is to get as many kills as possible (while maintaining a high accuracy) while completing the chapter in the shortest amount of time possible. Obviously dying is not an option. After youve finished the chapter, save and quit, and redo it again.
Note that the LENGTH of the chapter is irrelavent, its your rank at the end that matters, so pick one of the shorter ones so you can grind it faster.
You can also get points from playing mercenaries, getting a high rank in a merc level grants good points as well, however depending on your own personal abilities the first solution might be your better choice as merc can be difficult at times.