Question: I am a Trinity grade 5 pianist and have been playing piano for 2-3 years(earlier played keyboard).

I find very difficult to sight read. I usually play the passage once very carefully and memorize it well so I don't have look at the music while playing. I play while continuously looking down at the keys and find it difficult to lift my head up and register the notes and then play. I know all the notes on the staff, but I can't register them in time to play them on the spot.

What should I do to get better at sight reading?

Answer: 
As with anything, it will improve with practice. And, as with anything, *you should tailor your practice to the problem you're having*.

Since your problem is looking down at the keys, devise a practice method that prevents you from doing so. My teacher growing up always held a notebook above my hands so that I couldn't look at them. Do you have someone in your household or school that would be willing to do that for the 10 minutes a day you practice your sightreading? If not, you could always try rigging something to blog your view. (Or you could really be ridiculous and get one of [these](https://rads.stackoverflow.com/amzn/click/B076VYRT1B).)

Once you've mastered this, you may eventually have a problem with not looking ahead while you sightread; to address this, have someone cover up the current chord you're on, which forces you to look ahead. And so on.

See also recent responses to [What is a good way to practice piano sight reading?](https://music.stackexchange.com/questions/65879/what-is-a-good-way-to-practice-piano-sight-reading)
Would my approach be of any help to you?

I'm doing Grade 3 exam piano pieces but my sight reading is poor. I suppose it can be explained. I spent many hours practising and polishing pieces. Comparatively, I worked relatively little on sight reading. I'm now evening up the emphasis and I hope it will pay dividends.

To train, I think you have to avoid becoming familiar with the music. So I have bought lots of short exercises (over 100 in all) and I play them at random. If I am in danger of knowing the music to the point where I can play from memory, I stop playing it for a few weeks which usually does the trick. This is different from reading the notation as one would the text in a book. I really want to develop the skill where you read the notation and hear the music in your head without playing a note on the instrument. 

There are various method books, YouTube videos, phone apps and books of practice pieces at the right level out there. I had to experiment to find what worked for me. I have not found a magic method that doesn't require a lot of work. I'm on my third method. It has taken me a while to get here. I am now happy enough with the method that I decided to stop looking for a better (magic) method and just get on with it. 

I set myself an aim to practice for at least 20 mins every day. It takes a lot of mental effort, so I make sight reading practice the first exercise of the day. If it goes well I might do more; if it goes poorly I might go back to simpler exercises or stop after 10/15 mins if my head just won't take it in. I found sight reading exercises too hard to be tacked on to the end of practice after working on exam pieces and technical exercises. 

Hope this is helpful for you.