Art should always be framed - even canvasses should have small wood frames. Look for a frame that has a small gap between the canvas and frame. While it's barely noticeable it gives a finished look without detracting from the painting. There is no one rule in choosing a frame. Keep in mind colours, size, ornate vs simple, light vs heavy, and to matte or not. Photography always needs a matte - in a shade of white is best. Prints and watercolours are best with a matte, though oil paintings can stand alone in a frame.
Frame should compliment and add value to the painting. Prepare and visualize the location of the artwork being hanged. Wall colours and furniture has to compliment with the artwork.
Especially in India, one should cover the artwork from the backside with a non-toxic paper. This avoids insects eggs or any mildew due to weather. Regularly keep check on the painting from back side.
To hang the artwork start by holding the frame at eye level - the centre of the art will be around the 5-foot mark. Then work your way up and down from there depending on the size of the piece or other items and furniture on the wall.