I have a pretty complicated system of planning (and executing) tasks for the next day. (The system started very simple about 2 years ago and grew organically with me.) My plans are pretty tight in the morning, when I want to do a lot of stuff very efficiently (my normal schedule from 5:20 to about 7:00 contains 8 tasks ranging from 1-2 to 25 minutes, has a resolution of 5 minutes and very small buffers until about 6:15, when it becomes a bit more lax), more lax from, say, 9-10 to 17-18 (usually tasks from 45 to 90 minutes, with 15-30 minutes buffers in between) and _very_ lax in the evening (1-3 tasks taking 5-10 minutes each). The system is heavily gamified (which works well on me, YMMV) and connected to Beeminder (note: I'm not affiliated with them, just a satisfied customer (and an author of one of the alternative clients)). One key observation is this: motivation is overrated, discipline is king. Another one is: plan for breaks and rest. And another: getting enough sleep is one of the top priorities. Yet another: consistency trumps short-term bursts of activity by a very large margin. (One of the key features of my system are generous buffers. Even if I fail to perform 75% of my planned stuff one day, it doesn't matter much in the long term, because it's just one day.) Also, measuring time you need to do things is very helpful when planning/estimating.
Just a few random thoughts - I can expand on every one of them if you want.