Exactly what resources do we have down here in Earth's gravity well that aren't available and much easier to mine in space or on the smaller planets? Now if the aliens happen to prefer nitrogen/oxygen atmospheres in our existing temperature and pressure range, then yes, they might come down and conquer us. But unless that was the case, they would probably just take all of our solar system's extra-terrestrial valuables and then leave. Why bother to even acknowledge us, let alone land and conquer?

the same could be said about any conquerers.. but what if the resource is biological matter?

Two good points. Slaves and the land itself (which is what historic conquerors pursued) and our biological diversity (which is not available only down here). Both are great answers to my question, so I fear that Mr. Hawkings may be right after all. Thanks.

Maybe MAD? Sure they're probably more advanced than us, but are they advanced enough to survive nukes?

How we can help a frog from under the rock, when rock is already fallen over that frog. No How. Sorry, I meant new know-how, call the gods, explain seriousness of situation. Find weakness which may be exploited by us. Leading strategists determine that war with such an advanced species will without doubt end humanity and or all life on earth - fire them all, they incompetent.

Its not reasonable to try to instill fear in an unknown enemy. Fear is an emotional response in them, not in yourself. You must understand their emotions (do they even have a concept of fear?). How much time do we have to learn about them before its too late, and what can you say about these aliens and their goals that we might have learned?

What sane alien species would even get close to planet with species happily nuking their own, only, planet? :)

Related That will scare them.

Why would you want to make them fear us? They have interstellar space ships - if they fear us enough, they'll just bombard us from beyond our range. A single interstellar spaceship travelling at a significant fraction of the speed of light would be enough to sterilize the whole planet. Quite the opposite, you'd want to appear as peaceful as possible! :D

its like humans and cockroaches. we can destroy them yet we fear them irrationally that we rather back off

What? The last time I checked, when people find cockroaches in their house, they call the exterminator. They don't abandon their old house and their whole investment to move somewhere else. Not to mention that we're talking about an invasion force here, not a lonely housewife. Does the US Army fear cockroaches? That's one strategy the "Insurgents" haven't tried yet! :D

so consider snakes. we dont know if they are poisonous so we try to keep away. Dont take it too literally. also if you can choose to not go to a place riddled with cockroaches im pretty sure you would. so thats the right analogy

Manage to learn their techology and use against them

It's spelled: Stephen Hawking

Tell them that when we first came up with nuclear weapons, we calculated that there was a chance they might destroy the entire planet, but we tested them anyway because we were really really mad at each other.

There was a George Carlin special some time before he died where he talked about all the crazy torture and basically gruesome stuff we humans do to each other and animals, and that only humans were the ones who came up with these kinds of practices. Basically he's last point was "and we wonder why aliens don't just go around announcing their arrival/presence".

show them the website peopleofwalmart.com that will make any alien race fear humans

Fear nearly always precedes an attack - think about Al Qaeda and their effort to instill fear in the US. Fear is the last thing you want these aliens to feel for us - a better tactic might be how can we get them to ignore us, or overlook us, failing that I would suggest we need to become indispensable to them, become so useful that they would protect us and even invite us along on the interstellar rampage.

Just direct them to turn on news about the election. I'm sure we could transmit a couple channels...

You assume they LIKE Earth. More likely is they see it has a 21% oxygen atmosphere and fear corrosion and fire if they come anyplace near the surface. They will see Mars or the asteroid belt as a far more habitable place. The Earth would be deadly to them.

They will naturally fear Earth because it has a 21% oxygen atmosphere. They will not want to deal with such a toxic environment. They will fear rust, corrosion and fire. They will avoid Earth for the same reasons we avoid going to Venus. The asteroid belt will look like a better source of materials

Just like to point out that every resource of interest to the aliens is present in far greater quantities in the bodies they pass on the way here than on Earth itself, especially to any culture with the technical know-how for interstellar travel. Conquering Earth is for ideological reasons, and not economic/material ones.