There's not a whole lot you can adjust to make PS1 games faster, but:
Settings -> Driver -> Audio Resampler Driver: change to nearest
Settings -> Driver -> Video -> VSync: changing this to off instead of on might boost performance a bit (but on other emulators it'll make them too fast, so don't forget to turn it back on)
Settings -> Driver -> Audio -> Audio Sync Enable: change to off, might give a slight boost
Quick Menu -> Core Options -> Frameskip: change this to a value you can tolerate
Make sure you're not using any graphical filters as well (due to black screens and performance issues).
Personally I just turned the audio resampler to nearest and turned audio sync off, and left frameskip off, and kept vsync on. Tearing is annoying, and I don't like frameskip.