Hi Sania! There are tons of methods of course, but this is what I have been practising:
- I look at my watch.
- I look at the key and time signatures, look for any changes throughout the piece, check the speed, look for repeated notes/rhythms in the piece, and look for parts that might potentially cause difficulty. This takes about 30 seconds.
- I play, out loud, the beginning few measures. Then I play through, silently (fingers touching the keys but not playing the sound), the rest of the piece. I do this because if I play out loud and make a mistake, I instinctively want to correct it because I know I am just practising, but I don't want to waste time doing this. When I come to hard parts, I play them out loud and sometimes 2-3 times if they are especially challenging. Then I silently finger through till the end and play the end out loud.
- I check my watch, then go through the difficult bits again if I have time. I try to figure out the best speed, usually the speed at which I can best play the hard passages.
By then it is usually time to go! Remember not to stop for wrong notes or rhythms, and to keep the time. My sight reading is usually horrendous

but I have earned high marks for it in the past because I keep the time and I don't get shy while playing - I act as though it is a piece I have played for years.
Another piece of advice. All year I have been sight reading from old Grade 6 books. The past week or two I have started Grade 7, and now when I do Grade 6 pieces once in a while they seem VERY easy in comparison. Maybe you should try this if you have some Grade 7 books lying around. And DEFINITELY practise from ABRSM Grade 6 books if you have them!
Hope this helps!