Eugene's observations

A decent new printer/copier/scanner will cost about £65 currently so should you ditch the old printer at the first sign of a missed line ?

No.  Although it is not worth spending too much time trying to resurrect a typical domestic printer there are a few things worth attempting before sending it to landfill.  

Particularly with printers that are not used frequently, ink that is jetted through tiny holes will coalesce to form a barrier.  The best way of keeping the channels open is to run a printer cleaning cycle (off the menu of the printer itself) every month when you do your normal computer housekeeping.

If you notice problems and have been through the deep clean function of the printer the next step would be to take the offending cartridge(s) out and, after carefully protecting your local environment, blow air through the hole at the top; if no ink drops out it is time to replace the cartridge.

The next step on all bar the cheapest of printers is to remove all cartridges and get access to the print head.  This is often removable and is now ready to be dropped in an empty margarine tub with a little rubbing alcohol or white spirit.  Woosh it around and give it a gentle polish up with cotton buds.  Now take it out and dry it off with paper towels.  If you have a can of compressed air squirt some of that through the orifices.

Reassemble the  head and cartridges then run another cleaning cycle.  If it doesn't work now, it really is time to reach for your wallet.