Mistakes

First Mistake
One of the first mistakes a lot of d.i.y.'ers do is overestimate their ability to carry out the task, which usually means that it all goes wrong and they end up not completing the task, probably a lot more common end than is admitted, I would think this most likely affects men, as women would know their limitations.
Second Mistake
I think that the next mistake d.i.y.'ers do is to use tools that are not quite up to the task, or should I say they are not of a quality to withstand the use they are being put to. A typical example would be maybe a screwdriver that has been bought from a stall on a Sunday market, okay for the occasional use, but when used for a prolonged amount of time will give up, or worse break. As an Electrician myself, I think that it is worth paying a little extra on good quality tools for the use they are required for. I am not suggesting that everyone runs out and buys industrial strength tools that professional tradesmen use, but some people may prefer this option, just be aware that some tools are of a better standard than others.