Since I don't present in public, I have to buy my female clothes while dressed in normal, that is boring guy clothes. Here's a few hints to those who may find this type of shopping necessary, but intimidating:
1. Scope out the store beforehand. Know where the things are that you are interested in a few days before going into shop
2. Read up about the clothes, make-up, etc. that you are interested in so that you shop prepared and have an idea of what you are looking to purchase
3. Go in just after they open on a weekday
4. I like to be well groomed and in business casual clothing (hoodies and sunglasses make me feel like I look like a potential shoplifter)
5. Walk confidently to the area that you are intersted in and browse for the item(s) you want. Smile pleasantly at anyone who looks your way
6. Double-check that the size is correct and that the item has not obvious flaws - who want to come back for a return. Use a basket so that you can fold the article into it and it won't look so obvious
7. Walk calmly to the register, smile at the cashier and make your purchase. You are doing nothing illegal, immoral or shady
All-in-all, you can get in and out in about 10 minutes and with each trip you'll gain more confidence and find that you can start to browse a little more leisurely and actually start to enjoy the process. Shop for pretty things at first if you want to look like you are buying for your significant other, but then go for it.
Good luck!