Tactics

Smart bomb usage

Your bombs are handy for clearing the screen when it all gets a bit too much. However, you don't get any points for enemies you kill with a bomb. If you're playing for points (and let's face it, who isn't?) then you're much better off taking out the bad guys normally rather than nuking them. Use as a last resort.

Circle strafe

One of the most basic moves which any aspiring GW:RE player should master is the circle strafe. This involves moving your ship around the outside of the grid, shooting in front of you as you rotate. Just keep moving around, and don't stop! As only a few enemies in the game move faster than you do it is possible to avoid the vast majority using this method (unlike in GW1). You'll still need to keep an eye open for Repulsars and Protons though!

After circle strafing for a while you'll find a massive cloud of enemies behind you. When the area ahead of your circlular path is clear, take the time to shoot behind and remove some of the enemies from your tail. The GW:RE enemies actually get faster over time, so if you leave the "cloud" too long then they will eventually catch up to you! Don't be afraid to use a bomb if it all gets too much!

Limitations

Your multiplier is capped. It won't get any higher than 10x, so when you get to that you should change your tactics and try to survive rather than take risks. Why risk dying and having your multiplier reset all the way back to 1x?

Likewise, you can only have 9 lives and 9 bombs at a time. It doesn't matter how many you deserve... if you currently have 9 lives or bombs then you won't be given any more. Sucks to be you.

Wiggle shooting

We're talking advanced tactics here. The best players in the world add a little wiggle to their shots by gently adjusting the right analog stick as they fire. This gives a larger shot spread, meaning that you'll hit more enemies in the long run. It's tough to pull off though, especially when moving through large clouds such as a swarm of mayflies. Keep practicing, you'll get it.

And finally... Fast reactions!

To practice this, try catching bullets in your teeth. Or playing Frogger on the highway. (Disclaimer: don't actually do this).