Stomping Ground - pretty straightforward, it's a land, but you only get one land play per turn, so you don't always want it in your opening hand PAY THE 2 LIFE!
Land Grant - Ideally you start with one Land Grant and no Stomping Ground in your hand, so you can fetch one right off the bat, thinning the deck by 2 cards.You DO want to play both of them, even though you probably will not play both lands, since playing the second one allows you to pull the land out of your deck to increase your odds of drawing something that you actually can play, like another cost creature. Not to mention, they help bump up the storm count, which is always nice.
Elvish Spirit Guide - The least flexible of our mana options, we want to do our best to use this one ONLY on things that require green (if we can help it) so this one is best used to get out Concordant Crossroads or Glimpse of Nature if we have a choice, so we can save our Lotus Petals and Stomping Grounds to cast Goblin Bombardment or card:Grape shot when we are ready to end the game.
Lotus Petal - what is there to say, it's perfect! It can generate whatever color we need, it increases 'storm count,' and it looks pretty! Try to save them if you have another mana source, but you may wind up using one for a Concordant Crossroads or Glimpse of Nature, and that's okay.