First Come, First Served

The flags have to be placed in a specific place.

There will be a colourful area on the ground, usually a blue coloured circle. That would be where the flags are placed.

Make sure you've also grabbed Halo Drops & Mop Up, because they're a breeze to do at the same time. (BTW....When you finish Mop Up, you'll get Field Promotion as the next quest in that chain. If you do, and haven't finished First Come, I'd recommend finishing this one, first. You can turn this one in & then hit Field Prom right after, as they're closer to each other.)

As noted above, each spot has a blue area - it's more of a glowing blue miasma marking the spot, rather than a defined "spot", just to clarify. Just plant the flag in that marked area.

To make it easier...here are the coordinates I noted at each blue area:

Southern Pagoda at 43.90/59.91 - reddish roof, right near water, with a few Spitelash flags by it, near the questgivers for the other two quests area, in their ruins - they're at 41.43/53.85, for reference
Big ol' Tower at 43.61/43.41 - as it says, it's a big ol' tower, hard to miss. ;)
Northern Vista at 45.47/38.47 - little Grecian looking ruin, tucked into base of a small group of rocks
All are, by definition, beach front property, so follow the coast & keep the water in site. :)

Each spot has 1-3 mobs you'll probably want to clear to get safely to the spots. They're level 15-16 spitelash naga.

Confirmed still roughly same areas & coloured "halo" ring for banner locations still there. They were purple-pink on my screen, looking similar to Elune blessing lights.