You can try frame skipping. But the gameplay will not look smooth.
Depend on what renderer you use, I suggest you to always use SoftRasterizer and not OpenGL.
Another suggestion is, go to your sound settings, and go to interpolation choose None (Fastest, sounds bad).
And this is another great tweak, go to your emulation settings, in the general, deselect the "Enable Advanced Bus-Level Timing" option. This will improve your emulation speed a lot.
Don't use any Bios cause Bios can make your emulator slower.