Practice seeing auras. Instructions on how to are numerous online and through books. Auras are energy, spirits and magick are energy. Therefore learning to see auras will in fact help train you to see other forms of energy such as spirits. Don't expect to see them crystal clear at first. You may only see orbs or outline in the beginning. But the more you relax and accept (and not fear) what you see, the better you will see on a normal basis.
Oh and nature spirits tend to hide in the environment. At passing glance you may think you see a face or full figure in a bush or tree, exactly the same color as it (like a chameleon), but when looking back, you see nothing even slightly resembling it. Poof! Gone. Then you shrug it off, and continue on and see it again, yet once more, when you stop to look, it's gone. If you don't just accept that you have a nature spirit watching you, you may feel like you're going insane! =)
I prefer leaving a pinch of natural tobacco as an offering. It's very easy to transport as well.