Few ideas.
It's probably worth knowing that sight reading and general ability goes hand in hand, I don't think at this stage you should be worried about sight reading. I would first concentrate on getting a grasp of both the clefs and then put this into practice by playing really simple pieces... You wouldn't first find out the English alphabet then try and understand the works of Shakespeare you'd be lost!
What I would suggest is find some easy pieces (some that you know how they should sound) practice actually reading music, that doesn't mean sight reading, that doesn't mean you even need a piano, if it helps write the notes down as you read them.
Also if you're an absolute beginner you need to learn rhythm and note values, if you don't have a teacher for this, listen to somebody play the song as you read the music so you can help identify the note values, rhythm, rests etc. (this can be done on youtube or something)
Lastly - and this I would consider as an advanced technique, is understanding how to sight read. Like many I would troll through a new piece, stumbling at parts where I can't read the actual notes quick enough because i'm reading - right hand d, f, left hand g, a, b, right hand a, c, e and what happens is your music catches up. You can't read ahead if you read this way. 2 main tips for advanced reading is
Read a few bars ahead, start site reading by reading 1-2 bars before even starting on the piano, then try and keep 2 bars ahead. If you can't do that, pick an easier piece.
2nd is don't try and read them as individual notes, recognise patterns, while it sounds difficult, you don't read words letter by letter? you pick out the main key letters and you recognise the rest, try and apply this to sight reading.
Hope that helps.