You can maximise your ROI if you use a leveraged product such as spread betting (tax free) or CFD's (similar but TAXED).

I know most people either don't think about them, or are scared.
BUT
Use them properly and you can 'Hedge' your postions, which eliminates the risk of losses and maximises your profits. Basically you can run your own hedge fund.

You can see the basics of how hedging works on http://www.ycmoney.co.uk
They also link to excellent tutorials and video help files on other sites.

I personally have investments in my Self-Select ISA, but I have found over the last 4 months that my growth on my hedging trades with spread betting has turned my initial starting pot of £500 into, as it stands, in excess of £14,000 which I think is great!!!