Quality refers to the surface quality of the print and not necessarily the strength. The best way to increase the quality is to decrease the layer heights and use a small nozzle, but there are a couple of other settings that can be tweaked when slicing.
Since FDM printers work layer by layer, the smaller these layers are, the more detailed the print and smaller the tolerences. Most standard printers can comfortably print 200 micron layer heights, others can get down to about 50. The smaller the layers, the longer the print is. A 100 micron layer height print takes just about twice as long as one with 200 microns.
Layer heights are also limited by the nozzle size. A printer with a .4mm nozzle cannot print 400 micron layer heights. A good ratio is to not have layer heights above 3/4 the diameter of the nozzle.
As mentioned above, the nozzle size can effect the quality of the print as well. The smaller the nozzle, the more detailed a print can be in the XY direction. If there is a wall on the print that is only .5mm thick, it will be impossible to print on a .6mm nozzle, while a .25mm nozzle will have two complete shells. If there are ever any holes on your print or text is not coming out great, it may be worthwhile to check if a smaller nozzle will get the job done.
There are settings within your slicer that will also help with the quality of the print. PLA and other materials should have an active cooling fan for the surface to be smooth. Lowering the infill overlay percentage will prevent veiny surfaces. It is also good to run the printer slow with a slow acceleration speed, especially on the outer shell. But remember, as mentioned in the Nozzle Clogs chapter, slowing the extruder down could require some temperature changes in order to prevent a clog.
And as mentioned in the previous chapter, post-processing is also another great way to improve the quality of your print.