it shouldn't be hard; one person has their time to speak or ask something (with the other person helping them), then the other person.. I think the person who is not as good should speak first because you can speak about more normal things, then more difficult things later when the other person has their time. Both people have to want to help each other, though..
Personally, I prefer to meet in person at a coffee shop or something if possible, but if you can't do that, Skype is ok.
I can do language exchange with you if you want. I don't have a Spanish partner :)