Well,.... probably the easiest way is to use the Glow layer effect. Of course you have to separate out the part that you actually want to glow (put it on it's own layer). Another thing to bear in mind is that sometimes if your having difficulty getting the type of glow you want, it may be easier to do it in pieces, meaning multiple layers. A layer or two for say a tight glow close up to the object itself and then maybe a couple others with wider (and more transparent glows). The glows are transparent so you can build inrensity with multiple layers as well as have a lot more control by affecting the level of transparency/opacity per layer. You can always do it by hand of course. just put the object you want to glow on it's own layer and then create a layer beneath it and airbursh in a custom glow. That can leave you with hard edges on your glowing object up close to it so you may want to address that.