Basic trouble shooting for people who aren't mechanics and have no interest in becoming one:
1. Does it have a spinny part that's not spinning, or isn't spinning the way it's supposed to? Look at it- is there anything stringy wound around the spinny part? Remove it. Applies to: vacuums, aquarium filters, blenders, and rototillers, weed eaters, and lawn mowers.
1.b Is there debris from the spinny part that is building up on an nearby surface? Remove it. Applies to: vacuums, lawnmowers, probably other things.
2. Does it have a part that air, water, or other materials move through? Look at it- is there a clog, even a small or flimsy looking one? Remove it. Applies to: lawnmowers, vacuums, pumps, probably more.
3. If it has a gas engine, does it have gas? The right kind of gas? Does it have oil? If it's electric, is it plugged in? Or is it's battery charged?
4. Does it have a filter? Is the filter dirty/clogged? Clean it. Applies to vacuums, pumps, and some small engines.
5. Is it electric? Is there a safety feature where it won't work unless a certain peice is in place? Is there something keeping it from popping up or into place? Remove it. Did a small plastic peice break off? Can you super glue it back on in a safe manner?
6. Are there fluid tanks? Do they have fluid levels between the empty and full marks?
7. Are there tubes and/or wires? Are they all attached and going where they're supposed to? If it has spark plugs, are they all where they're supposed to be? If it has belts, are they taut?
8. Are there bolts and nuts? Screws? Are they all where they're supposed to be?