It took me a while to get a handle on trying to determine what was mass-locking my ship. I just played and figured it out as I went. Obvious things such as what ship you're in will matter, but it's usually not too hard to quickly cycle thru the targets around you and get an idea. ("cycle next target" is very handy - essential, really.)
The number you see reported as a factor will begin to give you a clue too, as you gain experience.
Factor of 23: Oh look, there's an Anaconda just 1.2 km from my ship. Yup, that's the guy!
Factor of 17: that's a Python. These are a couple of numbers that I see when I'm in my Python. I hardly have to look anymore, having involuntarily memorized them due simply to hours-in-ship.
With celestial bodies, like
@Para Handy mentions, you'll see that putting them behind you is quickest if you put them "on your six" and right on the ship's plane (on the scanner). If that's confusing, I can post a pic that (hopefully) would help. A good way to practice how well you're doing this is right when you drop-in on a system. You should be able to see the difference in how quickly you put that star behind you based upon your maneuvers when you drop-in or when you break away from fuel scooping.
For large bodies, it can seem like you're attached to taffy for a long time, watching your ship's speed increase painfully slowly.
You're going to find that there are numerous things in the game that you'll get accustomed to as you play over time. I know that's not the most satisfying answer, but it really applies to ED because there are quite a few subtleties and intangible effects that, frankly, many of us don't understand all too well because we're not physicists, astronomers, etc.
This and the Newcomers forum are always a good place to ask questions, so don't hesitate...
Have fun!