This is something I wrote out for a fellow corp member a while ago and he seemed to understand it with ease so I shall post it here for others to use as reference.
If something isn't too clear for you just let me know and I can work at ammending it so it's simpler.
Anyway, here's a guide to understanding how d-scan works.
The fundamental thing to know about the d-scan is that it's based on the camera angle and the view you have on your screen. NOT the way that your ship is facing. So if you're looking at a planet that is your camera focus and what your d-scan will focus on when doing a 180 scan of the system.
Now, when you enter a system for scanning purposes most people jump to a random planet and whack out their probes but in this case you'll be using your d-scan. If you can see that people are in local and there are ships appearing on a 360 scan from where you are it's time to narrow that margin down.
So, make sure that you have the max number in the distance box for your d-scan...tick the box for selected overview just above it and make sure the slider for angles is on 360 and hit scan. That tells you whats in about 14 AU radius of where you are.
We are now ready to start narrowing things down, if you can see a Drake on your scan and want to find it narrow the slider to 180, if it's still on your scan great, if not move the angle of your camera and try again and keep doing so until you have it back on scan. Once you do narrow it down again to 90 degrees. Again if the Drake disappears, move the camera angle until it shows up again. Kep doing this until you have it between 5 and 30 degrees and it's still showing up.
When it's at that point look in space and see what icons are floating around, they could be in a mission/anom site or at a belt or at a planet...if they're at a pos or mission site you'll need probes. If its an icon for an asteroid belt warp to it and hopefully it was the right one and you get the guy. Sometimes there will be more than one icon to choose from and it's luck to find them but most people in low sec when it comes to a choice of a belt or a moon its usually a belt.
That pretty much sums it up, it's a lil confusing and takes some practice to get it but after a while you'll soon be tracking people down within 30 seconds of being in system
