For something that is likely to eventually wear out (such as socks, T-shirts, etc.), and is your favorite, do you:
Wear it more often! It's your favorite after all.
Save it for special occasions! It's your favorite, after all.
Institute a strict FIFO system so that everything gets equal wear.
Some other kind of rotation you will explain in comments.
Do not have favorite T-shirts/sweaters/etc. so this does not come up.
Any system you have is so completely haphazard and subconscious that you would be hard-pressed to describe it here.
Other, specified in comments.
(I have just this week completely worn out not one but two favorite garments--to the point where there is no point to donating them to any charity, as they would do no one more good than they have already done me--so I am thinking about these things at the moment.)