For the oxygen sensor, you just take it out and look at it. If the end is heavily covered is a black soot, then it needs to be changed.
The throttle body and Idle Air Control Valve will require a can of Carb cleaner. For the throttle body, you just unhook the air intake then spray some of the carb cleaner into it. Then wipe everything down to bare metal with a shop rag. Try to get around the edge of the throttle plate too. BUT, be careful not to get any cleaner into the intake manifold. It could mess stuff up if you do.
The IACV can be kind of hard to locate if you don't know your car too well. Once you find it, take it off completely and make sure you don't have any electrical components attached to it like mine does. After you take the electrical crap off or seal it off with a plastic bag, just spray down the inside of the iacv with the carb cleaner. You may want a carton of qtips to really get inside of it.
As for the MAF, you will need electrical cleaner. You have to be very gentle and cautious when cleaning this because there is a likely hood that you may break it. A lot of people prefer just to replace it.
If you want more detailed info, you'll probably be best off searching for information on your car specifically.
1. An o2 sensor is often bad long before the soot begins to build. The soot is a result of a long period of incorrect AFRs. Testing them is not something that's very easy to do, but they're fairly inexpensive, and should be done every 10-15k miles.
2. In the long run, carb cleaner can actually make a throttle body worsen. Same with an IAC valve. Carb cleaner does not dry completely. It saturates the metal, especially aluminum, and leaves behind trace elements, that form a sticky residue after a few heats cycles. Carb cleaner is made for use in *drumroll* CARBS!. In a carb, there is fuel present, with helps sweep that residue away before it has a chance to cause any problems. That's why they make Throttle Body cleaner. It's a tad more expensive, but it's the correct way to clean the IAC and TB.
3. Cleaning a MAF is not difficult, but it is risky. I don't know anyone who would rather replace the MAF than clean it. That's lunacy, and they're not cheap to replace. With Electronic Contact Cleaner, spray with the little red hose thing on it, from about 8-10 inches away. Very short burst, every few minutes. Set it down on something absorbent between spray. It MIGHT need 3, maybe 4 sprays to clean it good. Do not use it until it's completely dry. Some cars will end up idling and revving funny for several days if you put it back in too early.
Keep operating temps where they're supposed to be. Water Wetter is supposed to be used with water-only cooling systems, in race cars, and some high-water concentration systems. With some coolants, especially Dexcool, the mixture of the 2 will actually cause silicates to build-up in the channels of the radiator, reducing flow.
Most liquid enhancements for vehicles, are loaded with stipulations. Like oil additives, are usually for use with non-detergent oils. I don't know anyone who runs non-detergent in anything remotely modern.