My advice would be the usual - learn about the process by keeping notes, specifically the strength of what you put in is important, which can only really be calculated if you measure SG before the ferment and work it out afterwards.
If you know the strength, you can use the calculator (as described on the main website) to work out the strength of the spirit which is actually dripping out of the nozzle at any given time. You can then get a good idea of which parts are good and which are causing the bad smells and tastes.
It's also handy to try collecting in multiple containers, keeping them in order, and then comparing them all to see what the different smells are like. You don't have to do that all the time, it's just helpful to get it into your mind about what is happening.
Key part is that there isn't a firm line where one thing starts and another stops. It's a gentle curve, the first stuff is bad, then you get gradually less bad and more good, till the main hearts part, then the tails come in and you get more and more bad mixed with the good. This might help explain it:

Image borrowed from here:
http://homedistiller.org/forum/viewtopic.php?t=11913Important to remember - a little bit of tails will make a big difference to the taste, but if you collect the earlier tails (say 16, 17, 18 in the diagram) then you can make a run which is more hearts than tails, and it is worthwhile as you can then get a whole new 'curve' with pure hearts again. It's personal choice where the line is drawn, for speedy decent spirit ditch everything with tails in, but for more efficiency process them depending on how cheap you are!
