There are several options you can change to make playing PSP games much nicer:

1) Launch a PSP game and touch the screen for 2 seconds.
2) Edit the display and control settings.

Here’s what the settings mean.

Bilinear Filtering
Will smooth out the sharp edges caused by upscaling.

Right Stick
Allows you to set the right anaolgue stick to mimic another set of controls, including the left analogue stick, the D-pad, or the 4x PS buttons. (Useful for moving cameras controlled by the D-pad!)

Camera
Sets the camera to use the front or back.

Colour Space (PSP System):
Uses vivid colours added with PSP 3000 (Read more here)