opening for 1000 elo
There isn't like the best opening. A lot of them are good and it depends on your style. Maybe look on tier list which Hikaru made but look on this which is for begginers.
If I were you I would learn how to play Queen's gambit, Slav defense and caro-kann. I think better for begginers is d4 because after e4 ther are a lot of things which you can face and you have to know theory in all.
There's a lot of things to face against 1.d4 as well:
QGD, QGA, Slav, Semi-Slav, King's Indian, Nimzo-Indian, Benoni, Benko, Old Indian, Dutch, Modern.
At 1000, you should not be studying openings. You should be studying endgames. How to handle K+P vs K. How to handle a few pieces, like R+3P vs R+2P.
Then tactics and strategy. Leave openings for when you are 1800+. Until then, apply basic opening principals:
Develop towards the center.
Develop your central pawns and minor pieces first.
Get castled.
Do not bring the queen out early.
There is zero use in learning opening theory for 2 reasons:
1) You won't understand it. Openings are not about memorization. It is about understanding the point behind each move and what subsequent plans are. I am not a French expert from memorization. I know what White and Black must do subsequently and the reasons why certain moves are played.
2) At your level, no opponent is going to play the best moves, and if all you did was memorize lines, or memorize best moves, you will be just as clueless as he is!