Usually, your element is the one you feel most comfortable to work with.
I'd focus on learning to meditate first before you advance to asking your spirit guide to show up. It would probably make it easier that way. Meditate every night (or, as often as you can) for a week or two, then advance to asking your spirit guide to visit you.
Once you've gotten the hang of meditation and figured out what works for you, then focus on your spirit guide. Call out and ask your spirit guide to show itself to you, so that you can learn from it. If it doesn't work right away, don't get discouraged. Spirit guides have a mind of their own, and tend to appear when they think you need them, not vice versa. Maybe you will reach it through meditation, maybe it will appear to you in a dream, or perhaps you will just realize one day that you knew your guide all along, you just weren't listening. It often turns out to be an animal you have an affinity for (if your guide is an animal) or a figure that you've seen or talked to in dreams before. Sometimes it just takes an extra shove of realization to figure it out.