I play mid to highskill human myself and I can tell you what the nelfs do against me.
You have to know that eventhough a human can take his expo quite fast, it costs him a lot. First of all: milita are not free. They would rather like to chop wood instead of getting into militia form. Towers and tech costs a lot. The second point is that the fast building of the expo costs aditional resources. Last time I checked it cost me around 600-700 gold to build it with 5 workers. So eventhough the human gets ahead in time. You make up for it with the cost.
Either nelfs go and creep and take an expo themselves. The good thing about nelf is that you can make a tree of life next to an expo without actually creeping it. So what you can do is to set one up and harras the human while hes taking his expo. As soon as your expansion completes you can send your whole army to your expansion or even just send 1-3 hunts to help the tree to creep it by themselves. You won't get the item that way, but if you make sure to last hit the creeps with your units and not the tree. Your hero will get full exp. So what happens is that the human takes big losses against your harras and you set up your expansion peacefully. Ofc as a human you know that nelfs do that and you try to attack the tree before its completion. Sometimes even with 5-7 footies on themselves.
Antoher trick is to constantly scout with wisps where the human creeps. Dispell them on the water elementals that are tanking all the creep damage. You get bonus xp for your hero if you last hit the water elemental. The good thing is that now the units need to tank. When you harras later with your hero, you will appreciate all the orange + red health bars on the human units.
Some nelfs choose to go for a strong t1 attack. And I can tell you that it is not easy to defend that. Really dont know about the current patch but 2 years ago they either picked Beastmaster with mass hunts + glave throwers + eventually towers infront of human base or expo. It should still work with DH or KOTG. Just 2 AOW massing units. Most of the time you can end the game right there. But if the human survives you can start your tech at some point or do a proxy expansion and go from there.
I've hear that Demon Hunter is out of meta. But a lot of nelfs used to send a wisp in the human main while hes creeping. Then teleport with a staff of teleportation in the human main and use the fire spell. Kills a lot of workers and forces the human economy to stop working.
Some more tips:
Staff of teleportation is pretty good in that match up. You can
teleport to wisps that are close to the human main or expo, or to
your main base or your expansion. Costs only 150gold and gives you a
lot of mobility.
If humans do a full wall in their main. You can use a Zeppelin and drop units into their main. If he tps he might be in a very bad position or even cant get out after you left. He has to break his own wall then or buy a new tp (or Zeppelin). The point is that Zeppelins are very good vs human.