This for me is an interesting one since it also depends on what element I'm feeding from.
If it is Earth I am feeding from (the surrounding plants, animals, rocks, whatever that are around me) then I find the easiest way is simply to kind stretch out on the ground and first I listen to the sounds of life all around me. Say I'm in a forest...I zone in on the sounds of the birds in the trees, the creaking of the branches as they sway in the wind, the feel on the ground beneath me...eventually as I listen I will begin to pick up the smaller sounds...the insects in the bark of the trees, the leaves as they rustle beneath the weight of a single bird, the sound of a stream gurgling off in the distance. The more I zone into the sounds of life all around the more in touch I become with what I call the general spirit of the forest. I can feel it within me as I become a part of it. Once that connection is made mentally it becomes easy to visualize the life of the forest as it settles into you from the trees above and soaks up through your skin from the ground below. It is a gentle, calming and very relaxing feed.
If it is Fire I am feeding from, I stare at the matter that is burning...say it's a log in a campfire. I watch the embers beneath the flames as the red glow runs over the surface of the log, curling this way and that, until it seems almost to be a living thing with a mind of its own. I hold onto this feeling and visualize the fire itself as something of an entity all on its own, extending my hands toward it and feeling the heat of its touch. I close my eyes then and continue to hold in my mind the thought that this could be something like a being that is caressing my skin with warm hands. This all helps to solidify my concentration when it comes to extending a tentacle to that "being" in my mind's eye and pulling on its energy much as I would a one on one Psi feed from a distance. I let a little energy out, enough to form the tentacle as it extends from my hands to the warmth of the flame and then I allow that heat to travel back up into my hands and through my body. At first it can be a rather invigorating feed with a hint of excitement gained but the longer you sit there the more mellow you will become and soon you will feed warm and gooey inside, like you've just eaten a warm batch of grandma's melty fudge brownies. Or for those of you that are old enough to know what I mean, it feels much like you've had yourself a nice snifter of warmed brandy.
If it is Air or more specifically Wind that I am feeding from I find it to be a very easy feed. Perhaps it is due to my own odd ability to manipulate and direct the Wind itself. Though it is not technically my "element" astrologically speaking (I am on the cusp of Aires and Taurus so I am a mixture of the fire and earth signs as far as my personality goes...passionate but grounded...Yay me!) I do find that I have something of a connection to this element at all times. When the wind is going to blow I can feel it coming. When it gusts too hard I simply ask it to calm and it does. If the air is too still and stagnant I ask a breeze to come along and sure enough it will come. So I find this particular element and easy one to feed from as well. I simply call up a strong breeze by asking for one in my mind and as it blows I stand in it's path and let the gusts beat against my skin, simply soaking in what it has to offer. It almost reminds me of when someone pushes their energy into you. I don't usually need to pull anything in because it finds its own way quite easily. Much like the element of Air itself the energy it carries feels thin, as if it could weave its way between my very cells with little to no effort on my part. I can understand how it might not work that way for most though so I apologize if the description is of little help. The feed itself is, to me, a revitalizing one even though it is not terribly long lasting in its effects. It will always put a perky bounce in my step for a day or so though.