What works for me is picking a task that I estimate at about 10 to 15 minutes and just execute it. Even if it's just cleanup, or writing some docs, or polishing

What works for me is picking a task that I estimate at about 10 to 15 minutes and just execute it. Even if it's just cleanup, or writing some docs, or polishing an API interface. If I haven't gained momentum after finishing this it means that today is not the day and I'll retry tomorrow. But usually it's enough to get me started and pick up more serious things. 10 to 15 minutes is short enough to not feel negative about having forced myself to do it, but long enough for me to "get in the mood"