The best time to visit Sapa is from September to November (golden harvest season) and March to May (mild, blooming spring) for clear skies, comfortable trekking, and scenic views. It is a truly scenic place for photography - the top places to visit are as follows:
Sunworld fansipan mountain cable car ride. This is a must as you get to see a bird's eye view of the rice fields from the sky.
Rong May Glass Bridge. Walk on a glass bridge after taking an elevator to a mountain top. Be careful of putting your handphones outside of the glass rails as the winds can blow your phone away!
Cloud Yard, Ham Rong Mountain. This place is near the Sapa town and when you climb to the top, you can get amazing views of the Sapa town from a nearby hill. Its worth adding to your list of to visit places in Sapa.
Cat Cat Village. This popular tourist destination offers a look into the village life of the locals (after going down several flights of stairs) and is actually worth visiting because the village is situated along several beautiful river streams and waterfalls.
Silver Waterfall. This waterfall requires abit pf a climb up several stairs and is worth a look if you are a nature lover.
Avoid going during late December - March (Cold Seasson) where the rice fields are harvested and it is often cloudy thus obstructing the views. Also avoid Lunar New Year (Tet, usually late Jan-mid Feb) and long Vietnamese public holidays, as the area becomes crowded, crowded, and significantly more expensive.
Give Sapa about 5 full days (excluding travel) to explore the above and visit the various instagram worthy cafes/scenic viewspots such as Monan Sapa.
Always check the weather (to ensure no fog blocks your view) before going to any of the popular scenic destinations.
Cheers.