Use the thruster pack as soon as your sprint runs out. Then start sprinting afterward, around the time when your sprint runs out again, your thruster pack will be ready to be used again, just barely, without aa efficiency there is like 2-3 seconds downtime.
Its not exact, and there are still moments after using the thruster pack where you have to start sprinting again, but you are always moving quickly.
If you're looking to do any sort of quick forward movement on the ground you'd probably be better off sprinting regardless of whether you have mobility. Thruster is great for evading or changing direction mid air, but besides that its really pointless in my opinion. Thats not to say the AA eff. plus thruster isn't a good combo though.