How do i save left over oil paint so the paint doesn't dry up?

It's important to keep air away from the paints. Tightly sealed containers with as little air space as possible or plastic wrap laid over the wet paint on the palette. Also make sure you do not thin the paint with a solvent or another medium which would speed drying.

If you use a disposable palette sheet you can put your oil paints in a box and in the freezer, they keep for quite a while longer this way. BTW I like the jar idea though.

The best possible solution is to do what many serious artists, including myself, do: Don't buy or use paint in tubes. If at all possible buy it in resealable jars. Most art supply stores sell both acrylic and oil paint in jars now. As to the paint you already have you can buy small air-tight resealable jars from most artist supply stores to store the unused paint in. Or any clean resealable jar (empty baby food jars, empty spice jars, etc) will work. I went to the all jar method years ago when I started blending and mixing my own colors. When you mix your own colors you have to store them somewhere. So the logical step was to start using air-tight resealable jars. (By the way, Dick Blick sells the air-tight resealable glass jars, with lids, in 2, 4 and 6 ounce sizes. The jars, with lids, cost about $1.50 a set. But, as I said, you can use any air-tight resealable container.)

You can cover your oils with plastic or foil but the thing about oil paints is that they're just a drop of turpentine away from being less viscus. You can mix Linseed Oil into Oil Paints to thin them and change their viscosity and you can break oil paint down with turpentine or white spirits. If the paint gets really dry (Technically Oil Paint doesn't "dry" but that's besides the point) or hard the turpentine might not do much; however you have to be a SLOW painter. A puddle of Oil Paint will be wet for quite some time; it won't dry fast like Acrylic. If your palette is small you can keep it in an airtight container and try to get as much air out of it as possible and keep it sealed. Oil Paint hardens via slow chemical reaction with air so if you keep it sealed it'll be wet for weeks.

I used to store the left over oil paint in a plastic paper and keep it in the refrigerator.

Well, in my Art class my teacher told us, when we have left over paint in a tray (I can't think of the precise word right now), to cover the tray with a type plastic wrap. The type of the stuff you'd wrap your food in a tray so it can stay good longer. This method worked very well for my Art class. I hoped this helped! =]