Each NOTAM is given a radius of influence. For a navaid it would usually be the published range, for an aerodrome it is usually 5 nm and for danger areas and suchlike it will extend beyond the boundaries to provide a buffer.
If the circle described by the ROI cuts your route it will be included in the Narrow Route Briefing. The default for your route is 10nm either side of track.
You will also get NOTAM for your departure arrival and any alternate aerodromes you have specified.
A week ago I was asked by someone why he got BIG in his brief even though it was in the opposite direction to where he was going. The answer is because his departure a/d was within range so he could have wanted to use it as a navaid.
One gotcha worthwhile knowing about. If you cross an FIR but have no waypoints within it, eg. EGTR DCT LAM DCT LYD DCT EBCI you MUST include the crossed FIR in the appropriate box.
This route is Elstree, Lambourn, Lydd, Charleroi and crosses the Paris FIR but has no ICAO indicators within it. Stick LFFF in the additional crossed FIR box to make sure you get the LFFF NOTAM.
Re unlicensed a/d's. Chris is right, Popham for example is EGHP and can be used in a NRB, however it is unlicensed and has no ATZ. You won't therefore get an a/d NOTAM but you would still get normal Class G NOTAM, e.g. a Nav Warning for parachuting.
Mike