“If you haven’t used it in a year, get rid of it”:
This is very useful for items intended for every-day use in your life. Clothes are a wonderful example of such items. If you can’t find a reasonable time to use an article of clothing in one full year, then you’re probably better off without it. At the very least, replace it with something with more versatile uses. More formal wear than you realistically use? Get rid of the items which you don’t enjoy how they look on you.
This doesn’t have to be hard and set in stone, though. Have you realized you own more t-shirts than you use? Instead of specifically forcing yourself to get rid of the ones which haven’t seen use in a year, give yourself space to decide. Have a specific number in mind before you start cutting out; “I will get rid of 5 (or 3 or 10) this year.” Then, feel free to pick whichever 5 you like the least. Afterward, promise yourself a revisit to the t-shirt collection next year. In the intervening year, you may find you’ve come to enjoy one of the shirts which had been previously lost to the bottom of the drawer.
“If you only keep it because someone gave it to you, give it up”:
This one is fantastic! The fact of an item being given to you, no matter who the giver was, holds you to no social contract to retain the item. If you have a desire to keep whatever it is, independent of it having been given to you, then cool! This means whoever gave it to you did a very good job of picking their gift for you. However, if you are keeping something due to a feeling of obligation, get rid of it! You do not have an obligation keep a material possession, no matter its origin. You should be keeping only those items which are of use to you; those items which add value in some form to your life.