Even I am a great protagonist of solfege and ear training I would like to complete the other answers and comments telling what I still practice everyday (even independent of the absolute sound and pitch of the notes I'm reading!) Of course the pitch of the note and the question which key you have to press down is the most important aspect aside of the note length and the fingerings. But there are some other things you can practice without out sitting at the piano:
analyzing the piece: parts, motifs, phrases, figures (give them a number, a name, a term (formal analysis)
analyzing the chords: chord names and Roman numbers (harmonic and functional analysis)
analyzing the rhythm: make a reduction of the rhythmic 8( and also of the melodic motifs, play the rhythm without an instrument (practicing the l. and r. hands just playing with or without fingerings).
In German we have an expression for this kind of training:
"Trocken-Schwimmen" (= "dry swimming", that means swimming without water, as some trainers teach swimming outside of the pool. That's the way I've taught myself crawling at the age of 50!)
You can call this also brain-gym, cross-crawl, mental training, (mind that a good training of your memory also is a condition for sight reading.)
What I'm proposing is what I do everyday - and night! (with and without sheet music ...)
You can imagine that the benefit for sight reading must be great, when you look at the sheet music and you can easily detect the harmony, the chords, the rhythmic patterns, because you have a term for each element, phenomena and appearance and you also have the skills to cope the technical problems.
Can you please recommend me on books for advanced beginner? For example moonlight sonata is the kind of piece that i can read well.
The music I am learning or practicing is still the same I was playing when I started piano playing: Bach Inventions and Bela Bartok Mikrokosmos.
At the moment I practice these elements with the invention in a-minor and BWV 999.
(A technique, that helps me to develop my skills is also to transpose these pieces in C-major (as this is to me like a root scale), or changing the #-assignments in flats (parallel key) or playing it through all keys. A-propos scales: of course playing scales and chords in all keys is a very helpful to acquire the skills of sight reading, fingerings and all kind of technical (rhythmical and melodic) problems.
I train first the pattern with the hands, than with the fingers (if possible):
BWV 999 is a good example. (about the voice leading and the chords I still discover new aspects ... after playing this piece for 10 years now! but I know every single new aspect I find out will be a benefit when reading a new piece (transfer of learning!)
What I'm also doing is: I notate the new insight as a memo with the date and on the sheet or in a booklet. So I get a whole diary of the development of my skills I have got and my discoveries I have got.
Try out the preludes of the WTC (C-major, C-minor, C#-major, D-major, D-minor), the Inventions and sinfonias, and later the fugues. Suddenly you will see that you can sight read Chopin.