Good advice. 

If you stick a fairly large guage needle in it first, you can see if there is pus in it before you lance it.  If you lance it, make sure the hole you make isn't so small that it seals up again.  If so, it will just fill back up again.  The idea is to get it to heal from the inside out, so it doesn't re-form.  It doesn't hurt to flush it out with a syringe or two full of water when you are getting the pus out either. 

I wouldn't bother with a small lump though, unless it was an obvious abscess. 

Do you see this happening a lot?  I know some clostridial vaccine is just terrible for bumps and lumps, but they are usually reactions, which go away on their own, not abscesses.    Ultrabac usually isn't as prone to bumps as some other ones though.