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The druid is probably the mage hardest to rush, since either you focus the mage and leave the tree alone, and just let the mage transfer 2 life to the tree every turn, or you would have to spend about 2 big attack spells against the tree (which are attack spells not directed against the druid).
In my experience with the druid, I had the hardest time when I played against a warlock pentagram book. With so many thing with flaming attacks (the mage, the imps, the hellions and Adramelech), I was just lucky enough that in response to the bleed I got on my opponent she tried to drain life exactly to my reverse magic, which basically killed the warlock with a high roll (exactly when I was sure I was going to lose). Solo warlocks were easier to deal with.
My first turn is usually use the leaf ring + vine tree (so I stay with 19 mana for turn 2).
If my opponent seem to try to rush my, I bring a mana flower from the tree, a 2nd level animal (usually either an emerald tegu or a timber wolf) and a defensive enchantment (usually rhino hide). Turn 3 might possibly include a tanglevine on enemy mage during deployment (to keep him out of range 2 from the tree), and sometimes the vinewhip staff to make shure he stay stuck (astral anchor+arcane ward it usually a good follow up).
If my opponent seem to go for a long game, I have 2 options depending on which druid book I use, either mana flower deployment + samara tree + sunfire amulet (in my double tree book), or mana flower deployment + another mana flower + facedown enchantment on my mage to be used later.
Usually I recommend new players not to play with or against the druid in their first couple of games, since it is sort of an advanced mage.