To draw an attractive posster u have to remind the following points
1. make the borders attractive my cutting them in diffrent shapes
2.use only bright colors while writting something or drawing something
3.Highlight the main topic so that every body can watch it clearly
4.paste or draw some pictures related to it 
5.don't make posters on white chart use colorful background 
6.Use poster colors and pencil colors toghether use pencil colors for shading and poster colors for coloring