I finally feel like I have something worthwhile to contribute here as I'm in my own last few years before leaving my career. Currently about two years out, and planning to give a pretty long notice because of how tied in I am to many processes at work. I like and respect my boss and colleagues and would like to smooth that transition as much as is reasonable. This will all conveniently line up with the completion of a very large and complex project, so it will be a good time to depart.
Keeping up my motivation is something I think about all the time. The pinned 'pre-FIRE checklist' in this forum has been a great starting point, and I set up my own version of that list in a spreadsheet, then organized it into phases of a sort. In my case it comes out like this:
1 - research/planning ... this involved tracking my budget as carefully as possible for one full year (highly recommended!), setting up a master spreadsheet that incorporates all of those numbers and further estimates and goals, running numbers in every calculator out there, etc, etc. Lots of items in this phase but I was able to tackle them very quickly other than the one-year budget tracking.
2 - changes/preparation ... my current phase, and a fairly long one. Here I'm putting into motion the plan from phase 1, primarily adjusting my automatic savings and investment contributions in order to adjust my asset allocation over time to my target AA at my FIRE date (basically a 'bond tent' strategy based on info from this forum, Michael Kitces, and the excellent 'Living Off Your Money' by Michael McClung). Also lots of personal items such as several visits with a therapist specializing in occupational therapy and career changes (also recommended ... this really made me feel good about my plan and my thinking, and whether I was properly considering what will come next), getting a will in order, making sure all of my net worth goal numbers from phase 1 are being met and so forth. Still to go here is a meeting with a tax attorney to properly consider some situations unique to me, as well as having a call with a Vanguard rep and another independent advisor. Also a lot of reading through books like What Color Is Your Parachute, Lead Yourself First, How to Retire Wild, Happy and Free and things like that. Lots of great stuff to read and think about during my long commutes. Also, working on hiring at megacorp during this time, though my training of these new hires involves a lot of spreading my institutional knowledge around. Selling off stuff I don't need and decluttering at home. Diverting a portion of my automatic investment contributions into a money market in order to build up a downpayment should I decide to purchase a home (any mortgage or rent costs are already part of my expenses and future estimates).
3 - finalizing ... this will be the last couple of months before giving notice. Key is that I can still turn back at this point if I wish, but if I'm still feeling sure then it's time to proceed with maxing out all medical and dental options while still insured through megacorp: replacing older dental fillings that will need to be replaced in the next few years anyway, full physical and skin exam, getting my CV properly updated and in order, backing up professional contacts and other important details from work, making sure my retirement account contributions for that year are front-loaded and maxed out (I do this each year as it is ... megacorp thankfully offers a 'true-up' match), and so forth. Documenting as much as possible at work so this stuff will be ready for my colleagues. Writing a resignation letter. Last in this stage is setting my withdrawal plans into motion so that this income is flowing.
4 - give notice ... shortest phase of the bunch with a length of one day. :) No going back after this as I figure even if megacorp made me some ludicrously generous offer, I'd still be colored as someone whose heart is elsewhere at that point. In short, if I give notice then I intend to follow through.
5 - finish ... several months long unless megacorp wishes to show me the door right away which they well might as it's their prerogative. I expect to be very busy finishing this final project, and this might be the most difficult phase of the bunch. I expect a feeling of cold feet and second-guessing myself, and it might be difficult to stay motivated and work hard, all at a time when we'll be very busy at work in this last project. Time to put up or shut up. When the project is done, I'll walk.
6 - afterward ... move retirement account into IRA, start Roth conversions, etc. Take a long time off from all work. Further clean up my CV and consider my many interests and passions and what I might do next, albeit for much less or no money. I've no shortage of interests and hobbies and things I wish to do, and I can't wait to get to it all.
And so, having these phases above has been enjoyable way to keep my eye on the prize. I think about it all a lot, both just to work through any details I might be missing and also as a source of support when work is particularly stressful. I'm beginning to pass certain points at work which are the first of the "lasts", that is the realization that some upcoming work travel is very likely the last time that I'll have to travel to X, or that as we pass certain project milestones that this was the last milestone Y for me, and things like that. Those kinds of checkpoints give me a burst of energy, and I really need each one of them as I'm very, very over my line of work at this point. In my phone on a little note pad I have the words "prepare / replace / work hard", i.e. prepare and stick to the plan, replace yourself (with hiring and training and documenting), and of course the last part is self-explanatory. There's a long way to go, and all of this above is the structure I climb up and lean against for support.