If you don't use your printer for several weeks or months, this can cause ink to dry out and clog the nozzles. Inferior inks can cause clogging issues as well. Of course printer manufacturers will always tell you to use the right brand and formulation of ink, but it's not all just marketing -- cheap ink can cause all kinds of headaches with your printer, and might end up costing you more in the long run. Today's high-resolution inkjet printers have extremely fine ink nozzles; the inks are specially designed to flow through them without clogging, and to dry quickly on the paper without drying on the print head or in the nozzle.
When you find you do need to clean the nozzles, you can try several different procedures. The same cleaning cycle you used for the print head can be used for the nozzles. Also, check to see if your model of printer houses the nozzles on the ink cartridges or on the printer. If they're on the cartridge, and the cartridge is mostly empty, you can just replace it. The new nozzles will obviously be unclogged.
Seriously clogged nozzles can be cleared with some isopropyl alcohol and another run through the clean cycle. There are kits that will force the alcohol through the nozzles to clean them, although some people have had success using a dropper or syringe to apply alcohol, or filling an old, cleaned out ink cartridge with alcohol and running a cleaning cycle. These generally aren't "official" cleaning procedures, so proceed with caution: They could damage your printer or void your warranty.
The best way to keep your printer running smoothly is to avoid having to resort to drastic cleaning measures in the first place by using proper maintenance. Next, we'll give you some tips of cleaning and maintaining your printer.