Which season is best for planning vacations?

Depends on where you're going. Traveling "off season" can be less crowded and more affordable. Of course you might find yourself under monsoon or ice storm conditions. But at least your hotel room will be cheaper.

Summer

It all depends on your preferences. And also on what kind of vacation you want to get. If you do not tolerate the heat, then planning a vacation for this time is not worth it.

This totally depends on where to travel and what are your own likes. Some people like me love to travel in winters and some prefer the sun. So keeping in mind the destination choose your season of travel.

Any season as that makes no difference. I plan ahead and have been planning one in 2020 for a few months now. Haven't made plans for 2019 yet but I'm sure I will make plans when necessary, I want to start or decide on where I want to go.

Depends on where you are going and what you like to do.

Since we know nothing about you, we cannot decide for you.

The one you d the planing in. Three to six months before you desire to travel.

Shall we guess if you plan a skiing vacation on the slopes of Australia or Norway?

Maybe you want scuba diving or some mountain climbing. Maybe you want to explore some Garden in full bloom. They do not all bloom the same month all over the planet.

Shrek narrows it done very nicely for you.

My last vacation I picked a direction and planned day by day as I went until I decided to return.

Depends on where youre going. If youre crossing hemispheres, winter is a great time (because its summer on the other side if the world, so you can escape the cold for a bit), but, of course, summer is the tourist season, so you may find any major attractions overcrowded. Id say spribg and autumn would give a better balance in general between lower offseason tourist numbers, and reasonable weather

Maybe the Fall

Summer. No, winter. Actually maybe it's Spring? Let's go with Autumn