The computer won't be well cleaned if you'll use alcohol cleaners, you'll need to use a hard surface cleaner, in concentrated solution in warm water.

Cleaning the case
You'll need a cloth that you'll wrung in the solution you chose. Use this cloth to wipe the casing and all the external parts (cabling, keyboard). Make sure you wash the cloth since the soil will be considerable. Excess water shouldn't be used and try not to let water go into the vents of the case. You will be able to clean between the keyboard keys by using damp cloth pushed between the keys with toothpicks.

The following actions need to be taken every six months.
Cleaning actions that should be taken periodically, every six months

You'll need to open the case and remove all the dust from it and from the vents. You'll need to be very care full while cleaning inside the case. You can use the vacuum cleaner but be sure the motor is far from the computer and it's components. Also, you should earth yourself by touching any metal object that you know it's earthed, like a radiator.

You should vacuum the vents of the casing and the keyboard. The keyboard is a place where a lot of dust and rubbish collects, the amount might surprise you. Keeping the dust away from the vents of the case and the coolers inside it you'll prevent overheating the computer that leads to damaging the components. Also, it's not a good thing to push the dust out of the computer, it's just going to stay in your room and will eventually get back in the computer

Mouse cleaning
The mouse can be cleaned by removing the ball and dusting inside, remove stray food and human or dog hairs from around the rollers. You'll have to keep the mouse dry, everything has to be scraped out.

That's just a small bit of advice meant to help you keep your computer clean, it's a good thing to get your computer to a professional cleaning service for better cleaning.