I will either buy a copy of the latest edition of The Writers' and Artists' Yearbook or trot up to the library to use their copy. I will peruse it looking for publishers who will publish SF/fantasy and draw up a list. I will cross check the list against the fiction on my shelves and Amazon (co.uk) to see whether they publish my kind of SF/fantasy. These publishers will go to the top of the list.
For US publishers, I will consult www.ralan.com and likewise cross check against my books and Amazon (.com).
I will then rank them into some sort of order, based on how I feel they might respond to the MS.
Repeat above process for agents. (Does Ralan do agents? I'm sure I've seen a list somewhere.)
Then I will prepare sufficient versions of the synopsis and MS to cover all bases, e.g. short pitch, short complete synopsis, longer more detailed synopsis, first three chapters of whole MS, whole MS.
I will then compose a suitable query letter (designed to stand alone) and a cover letter (for sending with the longer synopsis plus 3 chapters) and start sending things out, recording what went where in my database. In doing this I will be careful not to send the whole MS to more than 1 publisher at a time (though of course it could be with an agent and a publisher simultaneously). As soon as it's rejected from one place, it will go out to the next place on the list, agent or publisher, as appropriate.
Whilst this is going on, I will be brainstorming, making notes on and producing a circular diagram for the next novel, which is completely different and set in the magic department of an FE college. I might possibly write a couple of other short things.
I don't find shorts easy. It takes me much longer to write 1000 words of a short story than to write 1000 of a novel. Then I can never sell the blessed things. Well, I haven't sold a novel yet either but I live in hope. However, my shorts are just not the sort of thing that is currently selling, so mostly it's a waste of time.
I do, however, find them useful for trying new techniques, e.g. odd POVs. Before I started Moving a Mountain, which is in omniscient viewpoint, I wrote an omni short story, during which I got a feel for how to make omni work. I think now I might just regard shorts as practice pieces and not really worry about trying to sell them afterwards. Unless one turns out well, of course. But even then... I quite liked the one about the musician and the apprentice assassin, but it was rejected as "too fluffy".