I'll be on this evening and would be glad to help with the Harvest Lord. My pyromancer is Kenneth DragonHeart.
Unfortunately, no one can help you with Golem Tower. You have to solo it. The good news is that it's a side quest and won't hold you back from otherwise progressing in the game. I suggest coming back to it when you're a higher level. (Though they give you the quest early, I know a lot of people don't complete it until they are at least level 10.)
Excellent question! But Im afraid theres no easy answer. This is definitely one of those YMMV things....
Because monsters will usually be added to a fight when somebody else joins, this can prove to be bad news for the first wizard(s). There have been times when I know I have health enough left to finish off a fight, so I dont bother to heal. Suddenly, another wizard pops into the duel, bringing with them a nice, fully-charged baddie! If I cant heal before taking a couple hits, Im toast - even though I would have won my individual battle.
If I see a battle in progress particularly one that involves the same creatures Im after Ill first try to quickly scope out the action. If it looks like its in the later stages (for example, if I see lots of pips), then Ill just sit it out and hope to join in the next one. If, however, it looks like the battle has just started, I usually ask if the wizard(s) would mind if I joined in. And, yes, sometimes I just run into the circle a few steps behind the initiator, without asking. Even if more monsters are added as a result, being there from the beginning can make all the difference -- both to the success of the endeavor and to how my participation is received. So far I haven't had any negative reactions -- and have actually made a couple friends that way!