Betting on singles is the safest way to bet, there's no doubt about that. The problem with Fixed Odds betting though is that for long term gain you have to be able to identify true "Value Bets". The reasons for this are given in our "Betting Advice For Novices" under the section entitled "The Problem with Fixed Odds Betting", and you may also find the section on "Value Bets Explained" useful too.
As for making profits with singles betting, even if you are lucky enough to manage making a profit you will find growing it a very slow exercise, certainly in terms of percentage gain. For us, accumulator betting is the best way to making big money, but you have to be careful not to be too greedy.