Oil paints dry for a long time. A recent painting needs light and air. To place a picture under glass, not under glass creates the greenhouse effect and the paint may flake off. A year after creating the picture, if desired, can be coated with a special varnish.
From direct sunlight the paint can darken, and some pigments fade. In a very dark place can yellow oil in the paint layer. It is better to place a picture under diffused fluorescent light or energy saving lamp.
Do not place a picture next to heaters and air conditioners to prevent cracks and sagging of the canvas.
To remove dust picture can be wiped with a soft dry cloth. If there are no cracks in the paint layer, can be cleaned with a well wrung out damp cloth. Detergents cannot be used.
If the slack of the canvas: if the subframe is modular, you can gently knock out the wedges; if the subframe deaf, better to call in a framing shop for restringing.