As always in a scientific presentation, the broad outline includes a statement of the problem, a description of the method of attack, a presentation of results, and then a summary of the work. But within that format, there is much scope for ingenuity. A poster should not contain a lot of details the presenter can always communicate the fine points to interested participants. In particular, it is not a good idea to present proofs, except in brief outline, unless the proofs are the focus of the presentation. The poster should begin with a definition of the problem, together with a concise statement of the motivation for the work.
Bulleted lists are effective.
An alternative is to break the text into chunks small units that are not necessarily paragraphs in the usual sense. For presenting results, graphs and figures easier to scan than the columns of figures in a table are even more appropriate than in a paper. Legends should be minimal. A brief description of the implications of a graphic, placed just above or below it, is helpful. Conclusions, again, should be brief, and they should leave the reader with a clear message to take away.