I could write it better myself
Fact or Fiction? Usually both
Even if you are an excellent writer, collaboratively written papers are usually better than a single-authored one if for no other reason than the content is better: it is better researched, more well thought out, includes more perspectives, etc. The only time this is not true is if you've chosen to group-author a paper that does not need collaboration. However, writing a good final draft of a collaboratively written paper does take work that all group members should be prepared to do. To read more about collaborating successfully, choose any of the items below:
Divide the Writing Tasks
While everyone is not necessarily a great writer in all aspects, they usually know what they do well. Someone may be great at organizing but not be a good proofreader. Someone else might be great using vivid language, but lose their writing focus. Have group members write what they're best at and/or ask them to read the first draft for specific things they know well.
Leave Enough Time for Revising
First drafts of collaborative papers are frequently much worse than first drafts of individual papers because many disagreements are still being worked out when writing. Leave yourselves, then, a lot of time to critique the first draft and rewrite it.
Divide the Paper into Sections
People in your group may know a lot more about certain topics in the paper because they did the research for that section or may have more experience writing, say, a methods section than others. To get a good first draft going, divide tasks up according to what people feel the most comfortable with. Be sure, however, to do a lot of peer review as well.
One of the advantages of group work is you learn to read your own and others' writing more critically. Since this is your work too, don't be afraid to suggest and make changes on parts of the paper, even if you didn't write them in the drafting process. Every section, including yours, belongs to everyone in the group.