These cards are all very complex; if I tried to write one article about the similarities of just Procession, Develop, and Graverobber; that article would be pretty bad. Procession and Develop deserve an article on just them, and perhaps Graverobber does as well.
The nice thing for you, at least, is that Graverobber is probably the easiest to understand out of all of these. If you can, just play a lot of games with Graverobber and no +Buy (and not Rebuild) and go for Graverobbers -- you'll get a pretty good feel of just how powerful it is at its best (it's not super-ultra-broken as payload, in which case it's a conditional gainer).
Without getting into too much detail (because that's hard), I'll say this much about Procession and Develop: do a check at the start of the game to see how "broken" they can be -- you want spammable (non-terminal) cards at appropriate price points. These cards do best when there's a lot of draw because gain-and-play gets really ridiculous with these guys -- you'll want to be thinking many more steps ahead than normal to make sure you don't waste any draw; think very carefully before playing every single Action card in your hand, especially cantrips, and especially when you have two (or three when you don't have cantrips in hand) or more Actions remaining in the case of Develop so you can do your mid-turn tricks...
Develop is really nice with cards that care about the top two cards of your deck (namely Herald and Wishing Well), and is really great when you can play it mid-turn because of the top-decking, so you'll want a deck rich with villages so you can afford to play mid-turn terminals that don't immediately draw you cards.
Procession starts to get better than "Throne Room with a drawback" when you can play the thing you gained on the same turn. I kind of already said that already. In this case, you'll be planning multiple turns ahead.
There you go. I will not be writing articles about these cards because I feel like I don't understand them enough. I feel like nobody in the world understands these cards to write an awesome article. Eh.