if you creating some art in 3D program or AE (which is only still frame - pic) or in any program that work with 3D space and DoF, its very hard and long to compute for it on viewing and rendering so easier way is to not create DoF inside that program and render final result out, put it to PS (photoshop) and create DoF there, if you know how DoF behave and looks you can create nice depth
just duplicate the layer, use on new one some blur FX (best is gaussian blur, its closest to lens blur, but if you got some other filter that can do lens blur use it) and very smartly erase the parts on that layer which you want to be in focus, use different opacity and softness to reach real result
repeat it one more time or few more times with more lvl of blur to reach more lvl depth ( depending how deep is your pic or how large is your focus distance.
you can do this ofc in regular PS work too if you create sigs or anything else w/o any other program
tip: read some articles with photo examples about lenses and focus distance, it will help you to imagine how different DoF looks like