Before I ever started cosplaying I'd made a list of characters that I really wanted to make if I ever got into it. I've added a few more to the list since then. But in December or January I sit down and look at my list and see what I have on my list. I kinda split them into 2 groups... Big builds (full armour, lots of complicated pieces, lots of techniques needed for them, and of course more money spent on it... usually 1.5k or so) and medium builds (few if any armour parts, not as complicated or in depth things I need to do or at least not as many of them, and a budget of like $500 or so) And then I pick 1 of each.
Last year for example I picked Samus Aran Dread suit (my big build) and Zero suit (my medium).
From there I figure out how I want to go about making the cosplay. For Samus I decided on doing EVA foam (since at the time no working 3D printer). I opened an app called Cosgear Planner (currently offline, may return eventually) and then created lists of everything I'd need to buy, steps I'd need to take under categories of like prep work (sizing the files in armorsmith, printing everything off, cutting the paper templates out), EVA foam (cutting out and gluing together each part), painting (heat sealing, plastidiping, painting). With that done I set about to get started.
I'd start with buying some of whatever I thought I'd need up front, and at least the most critical aspects. so like plans/templates first. This way I could get started with them. I then would use the guide to track what I had done, roughly how long I'd spent on it, to remind myself to take pictures. I'd complete everything in one category before moving onto the next. So no painting anything until all parts were ready for it.
So when I got to January of this year? Same thing. Look at the list, see what characters are there. I picked Spartan first as my big build and a second (that I haven't talked about since I'm still working hard on it and not sure if I'll even be able to finish it in time. Worst case I abandon it to make sure my Spartan is done.) And I've been following the same process for the most part (just this time with the closing of that app, I've switched to using an excel sheet for the time/task tracking). I have all the 3D printing done now so just making sure everything that needs to be attached is. Though I did kind of jump things a bit here and start sanding the helmet visor so I can get a local vaccuform tech to make the visor for me.