Purchase stencils at a craft store. You can buy individual floral stencils or themed stencils in kits with various flowers, plants and trees. Buy paint, a small roller brush and a stippling brush.
Tape the stencils to the wall, using cellophane or painter's tape. For a floral border, tape the stencils along the ceiling at the top of the wall. For murals, affix the stencils to the wall, and then step back to make sure you like the placement. For a garden look, tape various stencils along the bottom of the wall so that it looks like flowers are growing up from the floor.
Pour a small amount of paint in a tray. Go over large stencils with a small roller brush. Use any color you want for the flowers.
Paint smaller details such as the stems or centers of the flowers, using a stippling brush. Dip the brush into the paint and dab it onto the stencils.
Allow the paint to dry, and then peel the tape and stencil off the wall. Move on to another area of the room.