I've been investing now for almost 30 years and over that time it has become clear that investing for long-term gain doesn't have to be difficult or complex. In my new and fully revised investing guide, Multiply your Money*, I've endeavoured to show that while it's fun to try to beat the market, just like a seasoned Investors Chronicle reader, that isn't actually necessary. Market-average returns are actually fine, if you start early enough, invest consistently and keep costs low. For the less experienced it's a truly simple route to wealth creation (see 'It's not complicated'). For the more experienced investor, dealing with individual shares as well as funds, things are a little more complex. There are still plenty of easy mistakes to avoid. Here, then, are 10 common errors.