After reading this from Ace Your Face I have now discovered tightlining. If you don't know this is basically drawing a line from underneath your top row of lashes which basically helps fill them in giving the effect of more lashes.
The image below from Painted Ladies really best shows the difference between a non lined eye and a tightlined one.
It takes a steady hand and I think a gel eyeliner is best to get the effect right but it's nice and subtle and creates a really thin line which try as I might I just cannot do from above the lashes.
Please read the guides from Ace Your Face and Painted Ladies who will be able to explain exactly how to do it.