There are checks that you should employ on your table saw as you work, these will feed you a constant stream of information on how accurate the tool is. One of the most basic checks is to frequently apply a square to a ripped edge or crosscut end. If the square tells you the cut is not right, you know you must check to find out why.
Another simple cheque to use as you go, is to draw a crosscut line with a square. If the blade does not stay on that line as you cut, it's probably the mitre gauge that requires attention.
There are three important alignment rules that apply to any table saw; the table slots, the rip fence and the saw blade must be all parallel.
The rip fence, the saw blade and the mitre gauge head must all be perpendicular to the table surface.
When the mitre gauge is in the normal crosscut position, it must be at right angles to the blade and the rip fence. Assuming that you have already checked for parallelism between table slots and saw blade the zero setting of the mitre gauge can be checked with a square.
Since the blade, which is locked on the harbour, is the one thing of which you have no control, it's wise to start all alignment checks by determining whether the table slots are parallel to the saw blade. All other checks are made on the basis of this important relationship.
While these rules call for parallelism between the rip fence and the saw blade, it's not bad practice to be a bit generous at the rear of the blade so the rear teeth of the blade will not scrape the wood after the front teeth have cut. This kind of adjustment can reduce roughness in the cut and minimise feathering.