I had a go at sharpening and setting some of my carpentry saws – but needed some kit to start with, see below:
Some of the main requirements are: a vice to hold the saw blade firmly, a saw set (I bought this one for £2 in a car boot sale, needed some cleaning), triangular file (smooth, £1.50). I also found a hands-free magnifier with light useful (£11).

Modern “hard point” saws cannot be sharpened
with normal files, but they can still be set. So you may get more life out of them if you can check and adjust the set angle of the teeth. I won’t try to explain how to set/sharpen saws – it’s covered elsewhere. For example, the article on this web page: http://www.vintagesaws.com/library/primer/sharp.html , gives very useful information on saws, and sharpening/setting techniques.
The photo above shows the result of converting a cheap cross-cut saw to rip saw (more or less), by filing. A rip saw tooth “chisel edge” should be at a 90 degrees angle to the blade length. I nearly took this cheap saw to the recycling centre because it had never worked (kept on binding), but with filing and setting it now does a useful job.

Notes:
1) A cross cut saw is designed to efficiently cut across the wood grain (the teeth act like knives), whereas a rip saw is designed to cut along the wood grain (the teeth act like chisels).
2) The set angle of the teeth shown in the photo above is greater than might
normally be used. This results in the cut wood edges being “rougher” than normal, and the cut not so accurate, but the saw has less
tendency to bind.
3) If a saw tends to steer away from its intended cut line it could be that the set angles of some teeth are generally greater on one side of the blade than the other (and the blade tension may be too low on a bow saw).
I used the above mentioned “rip saw” to cut down a piece of tongue and groove plank to make a bow saw blade guard. A deeper groove was cut (arrow) to house the teeth.