First, we need to establish why the aliens invaded Earth.
Although it is possible that aliens have invaded us to take charge of our administration and help us, let us assume that they are NOT here out of benevolence. Alien biochemistry would most likely make terrestrial organisms (including humans) toxic to aliens, so we can be pretty sure that they aren't here to eat us. Any minerals or chemical resources that are available on Earth would be just as abundant, if not more, on other planets, so we can rule this out as well.
This leaves one likely possibility - that their home world was destroyed or rendered inhabitable because of some disaster, and since Earth has similar conditions, they are here to relocate.
The next question then is whether they are amicable to humans - being open to sharing the world with us, or would they consider us vermin only to be eradicated.
Since we cannot be sure, I think it would be best assume they are hostile, and go into hiding. I would choose a remote spot, far from any city, probably hidden in the woods. I would also avoid the seas in case the aliens decide to trigger tsunamis by bombing the oceans. You would need to go inland and find high ground.
Basic survival strategies would have to be employed. You'd need to collect food, medicine, and weapons. You'd also be wise to collect camping gear - tents, flashlights, ropes, knives, portable stoves, flint lighters, etc.
Then wait and see how the invasion plays out.
I highly doubt that even the combined strength of all of Earth's militaries would be any match for the technology of an alien species that has mastered interstellar travel. However, diplomacy may give us a chance.
If all else fails, H. G. Wells was probably right about one thing. Germs may be our best bet. While natural germs may not have any effect on aliens, given enough time, we could learn about their biology and engineer a synthetic virus to kill them.
I hope that helps.