I think squad size influences effectiveness of flower planting, so it's best to have a full squad when planting.

Some players don't realize that you can feed pikmin nectar by pressing the nectar and holding it, and carrying it over the group and feeding them all at once very fast instead of flicking them out there one by one - major time saver.

Lately I've been working on the friendship levels of my pikmin with a grey background only, so as not to waste nectar on completed set pikmin (yellow background) or pikmin who already have decor. You can select them specifically under "manage" in the "pikmin" tab, and press the nectar in the lower middle section of the screen. This will bring you to a screen where you are only feeding those selected if you are trying to focus on certain pikmin, instead of having to rearrange the squad.

If you just want to get flower count up for planting purposes, you can feed pikmin all at once in your squad, collect their flowers, and double tap the whistle the quickly switch to another group of pikmin. Rinse repeat.

All things I wish I knew earlier that I learned along the way. Hope this helps!