Actual clothes-related mitzvas: (feel free to add to the list if I left anything out.) Disclaimer- one should of course ask one’s LOR how to apply these.
1. not allowed to wear shaatnez, a mixture of wool and linen. Items made of wool would therefore need to be checked to make sure they do not have linen threads or linings etc. There are some clothing that are more prone to shaatnez problems and need checking before wearing. Some manufacturers use scraps to finish off clothing that may be problematic.
2. the most obvious, clothing should meet tznius standards
3. women do not wear men’s clothing and vice versa. This applies to also non-clothing, such as accessories and grooming behaviors, some examples that come to mind: women do not carry weapons, men do not dye their hair or wear wigs. (I don’t know what English barristers did if they were frum, perhaps in those times wigs were considered men’s items)
4. special clothing are worn for shabbos and yom tov
5. a mourner tears his clothing at the funeral, and does not change his clothing during the week of mourning. One does not buy/wear new clothing during the month/year of mourning.
6. One does not wash clothing or wear freshly washed clothing during the 9 days before 9 B’Av (due to mourning).
7. One does not do laundry during chol hamoed. exceptions for 6 and 7 are for small children who need constant changing.
8. During the period of mourning between Pesach and Shavous (popularly known as sefira), one does not wear new clothing that would require a bracha of sheheheyanu- generally said on items that are purchased infrequently that bring special delight when worn.
9. Kittle (white robe-like thing) is worn by men at Seder and on Yom Kippur, some also on Rosh Hashana.
10. Tradition to wear white on Yom Kippur, to resemble angels. see 9.
11. we don’t wear leather shoes on Yom Kippur or 9 B’Av
12. Men if wearing a garment with 4 corners, need to put tzitzis on the corners. It is accepted to purposely wear such a garment to fulfill the mitzva.
Anything else. It’s amazing how many mitzvas/minhagim there are with clothing!