In the startup menu, go to your VIDEO SETTINGS option, turn texture size down to 256 or 128 if that's not low enough.
Lower your resolution. Not as much of a drain, I prefer running at my native LCD resolution on my monitor, but that's only 1280x1024, so I won't benefit by running lower. If you're running at 1900x1080 or whatever, try lower resolutions.
Disable other skins.
Do NOT preload textures into memory. If your system is that burdened, you probably don't have the RAM for this.
In-game, go to your clipboard settings, graphics settings, and on the advanced tab DISABLE the detailed terrain, the water, everything except bump mapping (save that only if your system needs a couple extra FPS, it's necessary for flying and not hitting the ground). Click okay on that tab, so you are back at the graphics settings page again. Disable skins, weapons effects, GV effects, reduce your distance sliders. I would suggest hitting "Default" to get them to default first, then slide them towards "nearer" from wherever that position is.
Do all of that and it might look pretty bad (compared to what we have now) but it will run a LOT faster. That's probably about as streamlined as you can make the game. You CAN, however, streamline your windows as well but that is another thread entirely.
