If an alien invasion happened right now, what would you do?
Aliens don't need resources from us when there are billions of other rocky planets out there chock full of all the minerals and chemicals they can carry. Even organic resources like coal and oil they could more than likely make themselves, if they even had a use for such stuff. Their DNA would more than likely be different to Earth evolved DNA so they wouldn't want to eat us or our food. They wouldn't need slave labour since, surely, they would have built their own automated machinery and robot AI systems. In fact, I can't think of anything of ours they would want, unless a habitable planet took their fancy.
So either they want our planet, in which case we would all be dead before we even knew they existed, or they don't want anything and just came to say hello and want to see what we're doing. If we know they exist, it would be because this is indeed their intention.
So I, for one, would welcome our new alien overlords and would show them all how we humans can knit doilies and play chopsticks on the piano and do sums.
Presuming they want to conquer the world, I would probably just secure my house the best I can and at the first midnight go with my car on a supermarket and get whatever was left there. Then I would go at my house and secure even more so even I can't leave out and they would think the place is empty. I would stay there for as long as I can easily survive with the supplies I have and then after few months when things would settle a bit, I would start going out sneakily at night to possibly find any survivors wandering because loneliness would be unbearable.
If I found any survivor, I would spy on that person for a while and try to figure out if its a nice person or not. If it was a nice person and lost, I would take him to scavenge food from the surrounding area and bring it home. Then we would discuss together what would the next part be. Possibly make a group of people, find guns and take over a bigger area but everything in the shadows. After some time passes I would try to recruit any people from around and make a small town, being more exposed and try to expand.
Then lastly, we would try to find a way to defend ourselves against the aliens and try to contact other possible areas that the same thing happened to make a network and try to fight the enemies. The best tactic was to use their weapons against them. If our bullets wouldn't work on their metallic armors but we managed to kill somehow one of them, we would melt the armor into bullets and penetrate them easily.
This would be the first step to take back the world again.
Id shoot them. In a life and death situation you either die like a hopeless coward or you fight in which statisticaly speaking drastically increases chances of survival. Id also team up with a few military people and avoid large concentrations if aliens and humans. Humans because they are like magnets when it comes to attracting aliens looking to slaughter humans apparently. Basically lie low under the radar. Communicate non electronically with other rogue survivor groups to plan coordinated ground attacks.
I would contact them and try to reason with them. I know how to do that already, in fact I knew it last year at this time. I'm working as fast as I can. I will not answer any more "are aliens real" questions, and use that time to finish. Your question, however, is a good one. It's nice to have a plan for any eventuality. And I do mean eventuality.
I'm off the grid but even my small area would eventually become subject to their whims. I don't believe they can completely conquer us, unless they do it by putting something into mandatory inoculations, .... oh wait, that's what's coming isn't it?
Why is it presumed that they will invade. I understand that human kind will see it as an invasion because humans are a violent animal. If the aliens are capable of traveling to this Earth, they have already won. Most likely they will come for natural resources and humans are a useful cheap labor. I would guesstimate that about 25% of the population is useless and would be humanely destroyed and turned into a rich nutrient source for the remaining fit humans.
Personally, I would probably kill myself and not be bothered.