Can someone please tell me exact steps on how to get a Latios because ..

Train a sableye to level 45. It will learn Mean Look. Go into battle with whatever strategy you choose. Use Mean Look. I believe you already weakened him, so just throw ultraballs. LATIOS CANNOT HURT YOU!!!! All of his moves are Phychic, and Sableye is unaffeced by ALL Phychic attacks.

Goodluck!

Really, the only thing you can do is keep trying, and hope you get lucky... unless you have a friend willing to give up a master ball.

Assuming you have your masterball left, use it here. If you don't, get a ralts with the effect shadow tag or a trapinch with arena trap and train your ralts/trapinch up untill it is about level 60 without evolving it (this can cause ralts/trapinch to lose the effect shadow tag/arena trap). When you encounter latios, weaken it and start throwing ultra balls (if you want, you can use evasive moves such as dig to make is waste its pp before throwing balls too). Another posibility is to breed mean look into a dark pokemon and train it up 20-30 levels. This will take a while, but when you fight latios your pokemon will not take any damage (note that you will have to breed mean look through several pokemon).

Well if you have a master ball and if you have nothing else to use it on then use it if not then get it up some more levels or find a dark type pkm that can lern mean look.Or if you cant get a dark type go to route 11 and go in the desert place and catch a trapinch because they have an ability called arena trap that makes it harder for latios to run away.

Try the pokemon lottery and get your pokemon stronger mean look won't cut it ok?

When he is asleep just switch to a dark pokemon

Really, the only thing you can do is keep trying, and hope you get lucky... Unless you have a friend willing to give up a master ball.