Use decent cleaning supplies. Trying to clean the bathtub with an old falling-apart sponge and all-purpose cleaner is a lot more time-consuming and frustrating than just using baking soda / Ajax and a fresh sponge. You’re way less likely to ever wipe down the counters if all your kitchen rags are in a mildewy pile under the sink. Use a Swiffer duster instead of just pushing the dust around with a rag. You get the idea.
For reducing clutter: go through your stuff, take things you feel like you don’t use often, and stick them in a big plastic bin. Put that bin somewhere out of the way, like in your garage or the back of a closet, and set a calendar event for a year from now. Once that year is up, donate anything that you never took out of the bin. If you didn’t need it in the past year, there’s no reason you should have it (with a few exceptions, e.g. fire extinguishers).
Clean in stages, not room-to-room, especially if you’re in a rush because company’s coming over or something. Start by walking through and throwing out anything that’s clearly trash, then worry about clearing off countertops/desks/etc, then vacuum, etc. It’s no good having sparkling-clean windows if there’s still muddy footprints on the floor when guests arrive.
Get a sink strainer and one of those suction-cup holders for your kitchen sponge. It’ll keep your sink from being constantly nasty and backed up, and your sponge won’t be sitting in moldy-food-water. Corollary: don’t use the sink disposal as a substitute trash can, that’s not what it’s for. It will break, and your kitchen will smell like rotting food.
If you haven’t cleaned in a while, your place probably smells funky. Yes, even if you don’t notice it, that’s probably just because you’re used to it. While you’re cleaning, open some windows and boil a pot of water with some spices in it (cinnamon sticks and some sort of citrus fruit is a good one) to get rid of the stank.
Put an open box of baking soda in your fridge. It’ll absorb any gross smells from old food, just remember to change it out whenever you clean out your fridge.