You need a least one good suit. It may take a while to find the right one and pay for it, but make it a goal. It should be made of one hundred percent wool and be very dark. You can use it for a variety of situations including weddings and New Year's Eve. Buy on sale, but spend as much as you can for a top label. It will last for years. Your new suit should fit perfectly. This is key. Buy it where they have a good tailor. Ask around. Be sure to tip him. It will eventually pay off.
Buy a good quality white shirt. Be sure to buy the right neck size. Check with a tape measure. Invest in an expensive (about forty dollars) silk tie. Learn to tie a double Windsor knot. You will look great. You will also need a pair of dark dress socks and a pair of good dress shoes, preferably black. These should always be freshly shined and ready to wear.