I mainly play five string banjo, but do a lot of crosspicking too. If you are a banjo player first and also know a lot of chord positions throughout the neck of the guitar(and chord variations) , you will have a great and natural transition into cross-picking guitar.
If you play melodic (keith style) banjo, the transition will even become more interesting as your cascading chordal melodies can be applied to either the guitar or mandolin.
Finding and learning interesting closed chord positions throughout the neck in my opinion is just as important as the right hand technique.
Also where you choose to place your melody within the strings is important to the power and stability of your sound.
Avoid starting to cross-pick in the lower registers. Your tones will be uneven, dampened and not as powerful to the over-all rhythm.
The sweet spots on the strings are the 2, 3, 4 strings. The best area of the neck for sound is also at least about the third fret and up when chording arrangement are adapted to the guitar. The higher strings and upper kneck are by far the best for sound and projection.
Cross-picking, unlike flatpicking, is not as improvisational, it take more work and understanding of the positions and strings in which the melody can be placed in. The options are endless and it is a true artform of sound manipulation, that ends up sounding the best when it is carefully thought out and arranged ahead of time.
If you are a reasonably good banjo player, flatpicker, and chord expert. crosspicking is the place where all these disciplines come together in my opinion.
Good Luck,
Dewey