Since the hoe raises or lowers the ground, (at the cursor), to match the ground the player is standing on, It's best to stand in a single spot (and don't move).

click all around, overlapping about 1/2 the circle diameter each click, as you move the cursor away from the (stationary) player.

If there are high spots or low spots, you may have to address those spots with the pick, but for the most part the hoe works just fine as long as the player isn't running around all crazy (missing spots) and ending up standing on different elevations during the flattening process.

If you have to flatten ground farther than your initial reach, then move to another spot that you are sure is at the same elevation and continue that way until it's a big enough area for the project.

The hoe will only (i believe) raise or lower the ground a max of 1/2 meter, in relation to the spot the player is standing on, and any deeper or higher than that, the pick must be used (+stone) to raise or lower the ground (roughly), before using the hoe again for flattening to the desired level.