Cotton shirts should go very infrequently to the cleaners, or you'll be replacing them. The chemicals can give your shirts a yellowish tint, and the fibers are being deteriorated by the process used to clean them. If you do take your shirt to the cleaners, ask them to hand press rather than machine press. No starch also lengthens a shirt's lifespan. A better (and cheaper) idea for your shirts is to machine wash them and hang them to dry. Then iron them yourself. Don't know how to iron? Shame on you. A guy should be able to effectively iron a shirt, and indeed should do so before wearing a dress shirt.
Dry cleaning is rough on your wool knitwear, especially cashmere. You're better off using mild soap and water and handwashing it. One word: Woolite.
Your suits cost more than your shirts and your sweaters, and are perhaps what you are dry cleaning (and damaging) most. Once or twice a year isn't terrible, but if you're not wearing the suit a lot, probably unnecessary. First off, a suit should be hung on the hanger it came with (should be a curved wood with hopefully some width in the shoulders) in a place where it can get some air, not stuffed between other suits or clothes in your closet. Hang it in a place wear it can breathe for a day or so, then you can put it back into the bullpen. Airing it out lets the wool release any odors and wrinkles. You can also brush the suit after use to remove any loose dirt or dust. If you do have a spot or stain, go at it with mild soap and water. If you're not comfortable doing that, take it to the cleaners and ask them to spot clean the stain, telling them what the stain is from. For wrinkles, invest in a steamer, or let the suit hang in your bathroom while you run a hot shower so the steam releases the wrinkles. If you do take it to the cleaners, take both jacket and trousers at the same time, so that any discoloration happens to both equally, and ask them to hand press it. Find a good cleaner. You get what you pay for. A bad job will be evident by getting clothes back that have shrunk or don't fit the same, shinyness in the material, or marks left in the fabric under lapels, around buttons, etc.