For good music the guitarist need the right attitude and his guitar needs the right adjustment.
To set up a guitar is pretty simple and also brand new guitars often have to be adjusted. It is possible that they have not been set up correctly before selling or the transport and storing influenced several parameters in a negative way.
Although the neck does not offer many options for adjustment at first sight, it makes sense to to customize it to the string gauge.
Inside of the neck there is a truss rod by which you can adjust the bending of the neck.
While the first Fender Nocaster got along without a truss rod (and because of the solidity of the wood nevertheless still stay the same today), you can now find a truss rod in almost every guitar.
The direction to tighten or loosen of the truss rod varies depending on the manufacturer so its important to get informed about the right direction before you start to adjust the neck.
And one thing that really matters in this case is to choose the right tools. This may sound trivial but European and American manufacturers use different types of threads and with the wrong tool you might ruin the nut. Then you will have to change the whole truss rod and this is pretty expensive.
If you want to modify the bend of the neck you should adjust the truss rod only little by litte (quarter turn) and never use violence! The wood is working and therefore it will take some time until it adopts to the new situation.
Convex or concave
Adjusted correctly the neck should be a little concave. Concave means that the neck sags a little bit while a convex neck is arched upwards. The perfect bending should be quite modest so that you are able to put a pick with 0.010″ through the strings and the neck at the eighth fret while you push down the strings at the first and the last fret.
The bridge is important for the tuning of intonation and the strings height.
The strings height is right when there is no buzzing while distance between the strings and the fingerboard is as small as possible. In this case it is worthwhile to experiment.
To adjust the intonation you have to compare the pitch of the open string to the pitch of the string at the twelfth fret (please use new strings for this). If you are too high you have to adjust the bridge saddles backwards to lengthen the strings. If you are too low you will have to move the appropriate saddle forward to shorten the string.
The height of the pickups and thereby the varied distance to the strings can change the sound of a guitar.
Every pickup influences the vibrational behavior of a string by his magnet. In this context especially single coils may cause a problem that is known as “stratitis”. The magnet of a single coil that is too close to the strings will retard the vibration of the strings.
If you solely use the bridge pickup it might makes sense to set the other pickups lower or to remove them.
Amongst other things the Les Paul Junior is as popular because of its single pickup with a very special sound.