Heres the thing - You will lose. Repeatedly. Understanding loss is the first step towards not losing.
I personally do not recommend playing the game under difficulty 7. Other than that, dont enable any lobby options, pick a 40-60 planet map that doesnt look too confusing, (can recommend clusters, those are usually nice and easy to read, though on smaller maps can get a little weird). I wouldnt enable anything else in the lobby (other than all of the expansions, because those just open up ship types). This *shouldnt* be too nightmarish, though just the sheer amount of distinct things to keep track of can get pretty high. Below difficulty 7 the AI has some pretty big blinders on, so I would generally equate 7 with the 'normal' difficulty of any other game. Above 7.. well, there gets to be varying degrees of 'hard', and it starts scaling up kinda quickly.
Mostly, learning AI war is going to take time. If you have a strong strategy game base, it might take slightly less time, but its still going to be quite a few campaigns. My only real advice here is to remember to use all of your resources as you get them - Metal and knowledge do nothing sitting in the bank. But those arent your only resources. Ship caps and time should be used as much as possible as well. Fleets should be busy and turrets should be plentiful.
Remember that you can pause (default keybinding p, may want to check settings to disable pause filter and music stop) at any time to look at the situation. Usual reason I suggest this is to get acquainted with the hull types of the AI's shiptypes, and what will deal with them.
edit - it occurs to me this was posted in strategy discussion.. Sadly this area is kinda barren. I would probably recommend posting in Ai war general for the most part