There are four important tricks you should know.
Lag free gameplay:
The first one is: if you're experiencing lag in PPSSPP games, whether using the PPSSPP emulator or PPSSPP Gold emulator, go to the PPSSPP settings. Under Graphics, in the Framerate Control section, turn on the 'Auto Frame Skipping' option to play the game without lags.
Full-screen:
And the second one is: if the game doesn't fill the screen, just go to PPSSPP settings. Under Graphics, in the Screen Layout section, click 'Display Layout Editor' and turn on the Stretching Mode. This allows you to play the game in full-screen.
HD Gameplay:
And the third one is: go to Settings. Under Graphics, in the Performance Settings, turn the Rendering Resolution to 10x PSP. By using this setting, you can play PPSSPP games at the maximum resolution
Flexible controls:
And the fourth one is: if you don't like normal controls and prefer customized controls by the creator, you can change them as you like. Go to Game Settings > Controls > Edit Touch Control Layout.
Reset:
if you don't like any of the customization, such as controls, game screen, audio, background image, or resolution, just open the menu in the game and select 'Delete Game Config.