When I see a rise in it immediately, and I see potential for it to go up more. That's the perfect time to buy, and sell right when it is about to drop.
A rise can be misleading. There are always some small bubbles that could happen and then there could be a really hard crash. You will eventually lose money if you continue trying to get money this way.
You may not necessarily understand the trend completely without a lot more research, as well.