Used wood stain on a coffee table and it dried with spots?
Staining can be a very fussy process.  It's not as easy as they make it look in the commercials or on those DIY shows (if you want it to look good).  Preparation is key.  Any defects in the wood like knots, checks, sanding marks, etc. will only be exaggerated by the stain.  You should sand to at least 220.  Keep in mind that some woods, like pine, just don't take a liquid stain well at all.  For those, a gel stain would be better.  In general, a gel stain is a lot more forgiving for an even color appearance.