It mostly depends on the kind of light you have.

Mountain bike lights have a wide area beam. You're going to blind anyone coming towards you with the light...period, pretty much.

Most other lights have a "flashlight" style beam, where there's a main brighter spot in the middle. You want to point the light down at the ground and turn the light on, Then move the light up right up to where the bright spot stops standing out as a bright spot - and stop.

You can also buy a light with an optically shaped light like [MENTION=152773]noglider[/MENTION] said. The drawback is they don't put any light above the horizon which is kinda of weird - like if people are lit up you see their legs but not their face. And they aren't as widely available as other lights. B&M makes the Ixon IQ Premium. Has 6 hours of battery life, but some people think it's not bright enough. Specialized makes the Flux which has a shaped beam, and you can switch on a "high" beam, but it's pricey and it wouldn't hurt it to be brighter either. I use a shaped beam light (Philips Saferide, but they don't sell it any more) and a wide beam light on a very low setting.

It really depends on what kind of light you have now. If you turn it on and shine it at the wall, is there a much brighter circle in the middle of the beam?