Firstly, if ink is not coming through after installing a new cartridge, a possible cause could be because the 'PULL' strip has not been fully removed prior to installation, as seen below. Ink will not flow correctly until the cartridge chamber has been depressurised by the removal of the plastic strip. Even after removal, the air-hole can still be partially blocked by left over adhesive. Simply use a pin or other small implement to clear any remaining blockage.
If printer performance deteriorates over time, it may be caused by a blockage in the print head system. This can be a particular problem in the older Canon printers.
Over several years, dried ink builds up within the print head and narrows the nozzles. Not only does this mean that a complete blockage is more likely to occur, it also makes it more and more difficult for the inbuilt cleaning cycles to clear any blockages. More often than not, once this occurs the nozzles tend to block straight back up as soon as they are cleaned.
There are a number of things you can try to get some more life from your printer.
Firstly, run three deep head cleans in a row - Without printing the 'Nozzle Check' in between - this will cause some pressure to build up in the system and is usually sufficient to clear any particularly stubborn blockages.
If this fails, to rectify the issue you could try manually cleaning the print head (if your print head is removable). To do this remove all of the cartridges and lift the small grey locking lever on the print head, you should then be able to gently lift the print head from the printer.
*Manual print head cleaning should only be carried out by those who would class themselves as technically confident and is done so at their own risk. This is not a guaranteed fix and is not recommended on machines still within the manufacturers warranty period.
The best way to clean dried ink or clots from inside the print head requires a couple of tools. A bottle of head cleaning fluid (isopropyl alcohol), compressed air canister and a small syringe are beneficial. Place the print head on top of some absorbent kitchen roll in a small container before carefully filling the nozzles up using the syringe and fluid. The fluid will run through the print head, slowly dissolving any clots and dried ink. Repeat this process a few times before gently using compressed air to gently clear out any blockages.
If you don't have the tools above, sit the print head in a shallow (5-10 mm) container of warm water and leave it for a few hours. Please be aware, this process can cause the container to be stained so it is best to use something that you don't mind being discoloured.
Overnight the water should break down the dried ink within the print head and once it has been left to dry thoroughly should be back to full working order.