I'm pretty sure a lot of you know this, however I just discovered this today (maybe I'm a slow learner!) so I'll share it for those of you who don't:

If you want to tell how many turns you need to go to a system, right click on the system but do not release the mouse button.

The game will display the number of turns and the route to this system.

Then you can:

- Hover over an empty space, then release the right mouse button, your fleet will not move.

- Hover over other systems, each time the game will display the number of turns and the route to these systems, release the right mouse button over an empty space when you're done.

- Hold CTRL and do the same thing, this will ignore standard routes and go right through space.

Hope this helps. 

Took me month or more to learn some of this. The CTRL trick to fly directly somewhere, well over a year before I knew  about it.

Great tips!

Saved me from many useless colonisation, especially with slow factions