1st outdoor grow, not sure what to look for to no when to harvest

I have two different strains im growing, white widow and XJ-13 the white widow has only been flowering for about 4 weeks but the XJ-13 has been flowering for about 6 weeks and im really not sure what signs to look for when its ready to be harvested. Any tips guys? (ill be posting some pics soon)

The RIU search engine or google would work well for this basic of a question!

from what i have been told by freinds..... any plant no matter how well hiden or cared for stands much of a chance outside of your own garden..... if its not stumbled across by some light fingered knob-head then it will almost certainly become rabbit food....and if your lucky enough not to have that problem ....mould or mites take there toll just as your counting your chickens! as what happened to me.... "ermmmm fuck"... i mean my mate...well he's not a mate i only met him once in a pub....and the bigger boys told him to do it ... then they ran away!

plenty of topics about that, 2 of them in the first page...