[Oskatat]

go to the 'system screen' (you know, with the planets floating in space), select the planet and at the bottom right corner, click the fleet/planet with the red circle across

always useful if you just wanted that historical dig

also, at some point, you may just colonize some smaller plannets, or when you previously colonized them, and stop upgrading them. Maybe work on it untill you have defences up, but otherwise, it really adds to micromanagement. Next, dont work on more than 8 big planets at the same time (except the beginning of the game). Choose a few plannets for ship construction, make the rest science and ! stop building the science planets as soon as you researched everything ! . You may think more planets for ship construction is good, but if you need that many shipyards in the first place, you are doing something wrong