Format your memory stick to a FAT32 file system.For example you can take the large amount of game genie codes I posted a while ago and put it on your memory stick.With a FAT16 file system (standard format) it takes up about 140MBs. With a FAT32 file system it is only a little more than 20MBs.
All you have to do is plug your psp to the computer and back up all your psp files. Right click on the drive it shows up as click format go to file system and select FAT32.Then copy your files back.This file system load faster and small files take up less space (in as simple terms as I could put it).
Sandisk memory sticks cost less,and load faster than sony memory sticks.
Plus they come with a 5 year warranty.
TIP3 Incase you don't know you can change your psp's background with pspersonalize or wabs skin changer.
Wabs Skin Changer
For pspersonalize you have to put the picture on the root directory of the memory stick.There should be 12 bitmaps(.BMPS).the resolution of the images should be 300x170. It should be no larger than 150KBs. Also the images should in 24bit format only.You have to rename each picture to a number that corresponds to each month.The pictures shouldbe renamed as follows.
FILENAME -Corresponding Month
01.BMP - January
02.BMP - February
03.BMP - March
04.BMP - April
05.BMP - May
06.BMP - June
07.BMP - July
08.BMP - August
09.BMP - September
10.BMP - October
11.BMP - November
12.BMP – December
I can't explain exactly how to use wabs skin changer since I haven't used it myself but I read that it is better than Pspersonalize