It is a new year and a good time to make sure your PC is clean.
You can clean your keyboard and monitor just using a damp cloth and drying if you want with a dry one. (I would suggest first unplugging both units from the power outlet.) A softer cloth for both will work best. For dirt between the keys try using a cotton tip squab or use a paper clip to push damp rag between the keys. I would not suggest removing keys as some keys are really hard to get back on and some have small parts and springs.
To clean around the case first unplug the PC from the power outlet. Then you can wipe along and remove dust buildup. You can also buy a can of compressed air and blow in openings. Now the cautions on using compressed air. Never blow it at a person. When blowing at the computer keep moving it, as the air is very cold coming out of the can and can freeze the plastic and discolor and also has moisture that will get on parts and can freeze.
You can open the case (usually removing screws on bad, but there are many ways cases open. Then blow out dust inside and also clear the air openings from that side. Then close the case, wait a couple of minutes to warm and dry and then reconnect power and turn on. If the air opens (where fans draw or expel air) are clogged it will slow your machine down, so cleaning may well speed your machine up. However only blowing from outside will build up dust inside.
Do not open any sealed components like the monitor, CD drive or power supply. Also don’t blow the compressed air in the CD/DVD drive as you can knock the lasers out of alignment and will have to get a new drive. There are CD/DVD cleaning kits you can buy to clean inside the CD/DVD drives.