If you have something to say, say it. If you have an idea you want to write about, write it.
Planning is all well and good, but the greatest plan with no energy spent realizing it is worthless.
When yo have energy, utilize it. There is nothing quite like feeling inspired. You can write at any time on any day, no matter how you feel, but if you get bitten by the writing bug, go do it. Don't jut think about it; do it.
This is by no means new advice, even from me. But that does not mean I will stop stressing it. And since I'm guy who hates repeating himself, trust me that it is important. If you have been meaning to get around to saying something, just spit it out already.