In reasonably flat ground, you can take care of night-time monster spawns aboveground by placing a torch at all coordinates where X,Z are (..0 , ..0) or (..5 , ..5)
You're placing torches every 10th space North-South and East-West.
Then you're making the same pattern offset by 5.
This also makes a pretty diamond pattern of light when seen from above. It is also easy to do if you are watching your coordinates in F3, the debug view.
This is enough light to prevent spawns on any surface as long as the elevation change is no greater than 1 between a given block and any torch.
If the elevation change is a little too high, there will be much diminished spawns, but not zero. (A light level of 7 will spawn mobs, but at 1/7 the rate of a fully dark block - and most blocks will still be lighted at 8 or above.)
Not all trees need to be cut down, because mobs cannot spawn on leaf blocks. A tree trunk in line with your torches could darken some blocks enough to make spawning spots. Things that are not in line with your torches (not at coordinates ending in 0 or 5) are reachable in multiple ways by light and so can be ignored. Acacia trees can have spawnable blocks (logs) in the air, so need extra light in the tree.
I need help finding a good and efficient way to clear large amounts of land in order to spawn condition the areas around mob farms.
In addition to the lighting mentioned;
bottom slabs (or other non-spawnable blocks, tilled land/crops, and water [but see below] can be used…
[As a side note for lighting, my preference is for every 4th block diagonally (rather than every 6th) as the lowest light level is then 10 which is high enough it ought to prevent illager patrol spawning and the pattern aligns with chunk corners; this requires a torch on the surface (which is what I use at first) or a jack-o-lantern/sea-lantern-glowstone recessed into that space (replacing the block that supported the torch).
In addition to the pattern (about which I agree), this spacing works well for marking where to plant oak and birch saplings (ie north of every light) or spruce/small jungle trees (north of every light in every other row).]
For water, one must also light the entire volume of water in river biomes (and any water more than 5 below sea-level [default=62] in ocean biomes as well). [Note that ice trays/farms are fine (if not in frozen ocean or river biomes) as normal ice is a non-spawnable block.]
Acacia trees can have spawnable blocks (logs) in the air, so need extra light in the tree.
The large variety of normal oaks and dark oak trees can also generate with spawnable log blocks although this is rarer than with acacia.
For dark oaks this happens moderately often (but is generally easy to see),
for the large normal oak, very rarely (but occasionally inside enough leaves that a mob can spawn in full daylight and is nigh on impossible to spot).
If what is meant by "clear[ing] large amounts of land" is removing all the trees (and the wood is not considered important) fire can help (assuming doFireTick is true), but some clean up will be needed.
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WARNING: I have an extemely "grindy" playstyle; YMMV — if this doesn't seem fun to you, mine what you can from it & bin the rest.