Iron: You can use the same technique that you did with the BDU trousers, using tape and wooden hangers. Make sure to keep your iron on a low setting, and never leave the iron on the fabric for more then a couple seconds. The same thing goes for the shirts except you only crease the sleeves.
Females: There is a little elastic band on the collar, it is used to keep the shirts closed when wearing the neck tab. When the shirt is open the best way to hide it is to loop it around one of the frogs on your rank.
Shirt Garters: Shirt garters usually come in a pack of two or four, four is recommended. You can buy them at any Base Clothing Sales for less than five dollars. The are basically strips of elastic with clips on either end. They are designed to keep your shirt down and your socks up. Don't make them too tight, as occasionally a clip will let go, with obvious results.