Storing Negative Energy:
In order to do this you are going to need some form of object in which you can store negative energy within, and you will need to be in a bad mood, so that you have negative energy in order to transfer into the object. This object can be pretty much anything though most of the time it should not be made out of metal. This is because metal is not very good for placing energy upon, because of its metaphysical properties. There are also some other items that have cleansing, or transmuting properties that would not be the best to place negative energy within. Once you feel you are done you can stop focusing
Once you have the item place it within your hands, or place your hand upon it if it is too big, and begin to visualize your negative energy from your emotional state flowing into it. Take your time and focus on this for quite a long time feeling your negative energy drain into the object and powering it with your negativity. You are going to want to sit in this process for quite a while, but once you feel you are done you can stop focusing, and remove your hand from the object.
Now you are going to want to keep this object in a place where you will not need to interact with it that much unless you are adding more negative energy to it. Good ideas of places to keep it would be within a box, or wrapped up in black cloth. Both of these will keep the negative energy from interacting with the outside world, and will not allow it to affect anything else in your space. Keeping your object safe and other things safe from your object. Once you find a purpose for that negative energy all you have to do is bring that object into your magickal working allowing it to power it.