how do you cast the distance?

[Steven]

with my 8foot rod and my 4weight line. i can cast about a good 30feet. but on a good day maybe 36feet.

As an aside, I'd note a few things. For most people, a longer rod will cast farther - of course there are the Lefty Kreh's of the world that can cast the full line on anything.

Second, the greater the rod weight designation, the farther one should be able to cast.

Third, the action of the rod will also affect the distance. A fast rod (tip-flex) will cast farther than a slow rod (butt- or full-flex). However, you give up feel with a fast rod which makes the short game harder.

Finally, cast are measured from where you're standing to where the fly lands. If you are actually casting 30' of line, you are casting 47' (assuming a 9' leader). That's not half bad on an 8' 4 wt and is probably the maximum fishing distance anyway.