Level up your hybrid dragons first, as a dragon that has more than one element will count towards multiple shrines. So, if you have more than one plant dragon, think - "do I want to level up more plant, or should I level up a plant hybrid like poison as that counts towards 1 level 10 plant and 1 level fire dragon."Likewise if you level up a clover to level 10 as that is a plant/earth hybrid, a level 10 clover will count as 1 dragon for plant and earth and so on.
Also, if you have a hibernation cave it's good to keep dragons in there. If you don't need to feed all your dragons just yet, store them in there and level them up when you need to. Yesterday I had 1 rain dragon that was sitting at level 10, and I had a mountain in there that was only sitting at level 1, so I leveled up my mountain to level 10 so that it would match my rain dragon in my quest for a sapphire. I like to have 2 of every dragon so I can call on them in an instant when needed. I think I have 6 dragons in my hibernation cave that are only level 1 dragons. (It's strategic play for me as all my shrines are gold and I'm working towards my first level 20 dragon). Hope that helps