The easiest is to go through items that have expiration dates that should more or less be followed and then toss. Like a mascara that’s half-used from two years ago probably should get tossed 😛 After that, look for items you do NOT like – these are the things you bought, tried, and didn’t work out for you but you still kept. Put these in a box and donate or pass along to a friend/family member. Then you can start looking through products you use and products you never use – stuff you never use might be worth giving to a friend. If it’s that one red you love but only wear for a special occasions, obviously keep that!