try an make sure you both got different tones to your guitars as if you both sound identical an play the same thing theres a massive chance that your sound will turn to mud! try and avoid both playin the same riff together especially if its quite complicated. try and make it so in your songs one of you comes up with a melody line to put in here or there. or try and come up with somethin to fit in between the guitars. its wot my band does occasionally one plays on the beat the other syncopated (off the beat) when we get this down properly can sound amazing. however we only use this for song that suit it an judgin from your name this wont be what you want. just try and be inventive whilst playin behind the rhythm or riff, an try not to just do a solo as this can slightly lack structure tho used right has a good effect. if you cant really think of a melody a wah can help as you dont need to be that creatvie an it can be used as a background/rhythmic sound that helps to carry the peice. hmm thats all i can really think but experiment just get the band together and play and experiment thats the best way an the only real way to find out what works for you!