Collect your materials and design your pieces. The easiest, cheapest and most fun way of doing this is traveling between your local dollar store, flea market and yard sales, searching for the right objects to create your beast or character. Don't be afraid to change the design as you hold railroad spikes up next to the shovel and lawn mower muffler. Maybe those spikes weren't meant to be the pudgy dwarf's arms.
Lay out all the pieces you collected, the way that you think they should go together. Step back and contemplate your piece of metal yard art. The old saying is, "Think twice, cut once." Don't be afraid to take your time, though. Enjoy your favorite beverage and think it through more than twice, as you may find a more pleasing way to assemble your piece.
Don wrap-around eye protection. Use your right-angle grinder to cut, grind and wire wheel all the pieces you intend to use, so that they will weld together more easily. The cleaner the metal, the closer the pieces will fit together. This will make a major difference, not only in the ease of welding but in the durability of the finished piece as well.
Use clamps or wire to hold the first two pieces together. Don your welding helmet and leathers. Weld the first two pieces of your yard sculpture. Repeat wiring and clamping to weld the next piece into place. Continue until the entire piece is welded together.
Once your entire metal yard art piece is welded, clean all the welds with your 24-grit abrasive wheel. Wire wheel any surface that may inhibit paint from adhering to your piece. Paint all the pieces using disposable brushes, masking tape and paint markers to add features and separate colors. Generally, the brighter and more cartoonish, the better. Place your piece in your yard or on your sale table and enjoy the response your creation gets.