The energy that you can use to achieve specific goals or purposes is fueled by the emotional need that you have for that goal to be accomplished. Without the need driving your focus- your energy will be impotent. Learning to harness your emotional need so that it can cause the energy to effectively react to it is a useful, and important goal for anyone looking to work with energy.
Firstly, there are intensities and degrees of emotion. As well as different types of emotion. You should always use a type of emotional need that directly applies to your goal. Don't get angry and negative and bent out of shape and try to use that to fuel your need to balance out your relationship problems- you'll just overcast your will with more issues.
The intensity of emotion applies to how strong that emotion feels. Don't try to think to yourself some kind of fake happy thought and then expect it to be a powerful spiritual influence. Real emotion that feels strong is much better than contrived, fake emotion when generating need to effect the energy. You know what your needs are(keep in mind that the line between want and need is very fine- something that you thought you only wanted may be a need, something you thought you needed may just be a want. Only you can really figure it out, but remember that your needs are based on your emotional desire for those things, and on what it takes to fulfill your goals for your life.)
Additionally, when you meditate/focus- and you decide to back your energy with emotional need, pay attention to how the emotion that you produce feels. Does your emotion feel comparable to how you always feel? Or is it making a real, noticeable difference in your spiritual environment? Are there other feelings present that overpower the emotion that you are trying to produce? Always keep in mind the tipping scale between your emotion and your environment (both interior and exterior).
When I have meditated on a specific emotion within the energy, I have coupled it with a suitable, simple (non-distracting) visualization, which served to help galvanize my awareness of it. I choose where I will focus it spatially, which is usually somewhere around my body- and also depends on how I intent to draw the energy around me into that space. I will either draw up from the earth, or down from the air. Using either my base or the space around my forehead/head as the focus where appropriate. Using the earth in the example- I expand my awareness below my feet, to the space below me, looking for variations in my perception of the space, examining what those variations are. When I am satisfied with how far I have expanded my awareness and what I am aware of, I focus on the emotional need that I have at my base, with an emphasis on the will to draw energy to that point from the earth. I monitor how the collection of energy proceeds, to make sure that it is to my satisfaction, adjusting and fine tuning my will and awareness as I deem necessary to draw the energy that I want. Sometimes this energy becomes feel-able to not only myself, but to others around me. For instance, I had been drawing a lot of energy around myself in the car once from the air, and as soon as I felt myself come into contact with an acceptable intensity of energy my partner immediately said that it felt so much better in that area than the one we had left from (he didn't know what I was doing) - I told him that the change in feeling and energy was the energy I was drawing, and that it was coincidental that he made the statement as soon as the energy I was focused on changed. The feeling should not just exist as a mental projection, but you should be able to receive that feeling as well when you successfully draw it. After drawing a satisfactory amount of energy, I will then focus my emotional need into it, making sure that all of my focus involving the energy revolves around the emotional need. Putting more time into this is usually more effective. However, when I am finished, I simply remove myself from the state of meditation, trusting the energy that I have focused.
Hopefully each of you finds a use in understanding the importance of emotional need. :)