If you co-write songs with other artists, producers, etc make sure you have a split sheet in place for each song. This in effect identifies what portion of the song each writer owns and it must be signed by ALL writers. It's advisable to have this letter signed ASAP, even while in the studio. This way it is fresh in everyone's mind and leaves no room for misunderstandings. Have it signed EVEN if the other writer(s) do not want credit for their participation. Nothing can change a mind quicker than a song placing on the charts and or making money.