Well, let's start off simple... a K&N air filter to start is always a good place... Then, not knowing what your budget is... a set of shorty headers and a more free-flowing exhaust. There are plenty to chose from in the way of mufflers, Flowtech, Flowmaster, Dynaflow are among the more popular choices. Some go for the glasspacks due to clearances and like the sound. Some guys remove the catalytic converters. This may not be an option for you as you may reside in an area that does emissions testing/inspection. Which would entail putting them/it back on once a year.
Heads: You can spend a lot of money here... However, if memory serves, the E7TE heads can be ported and made to flow fairly well over stock, but, not great compared to some of the aftermarket heads. The best bang for the buck in Heads are probably the Ford GT40 "P" models, but they require a specific header due to the spark plug angle being changed. Great head, and can be had for under $500/set complete. Or, if money isn't an issue, go for the AFR 185's... about $1500/set complete... other options include the AFR 165's, the TrickFlow Twisteds, the Ford Gt40X303, Gt40Y303, the Ford straigh GT40's. The Gt40's and "P" heads are cast iron, the X & Y303's are alloy... as are the othe brands mentioned... There are others, Dart II, World products, Edelbrocks, etc... ok... this is where my knowledge toward trucks tails off... I'm more of a 'Stanger, than a Bronco guy up to now... These guys are great and can probably add better to the information I've put on the table... But remember, Broncos are not what one would call sleek and aerodynamic... so.... ok guys... I'm a-waitin on the flood gates to open here and correct my misinformation where Bronco's are concerned... I can take it... really... < cowars into the corner... >
Hope some of this helps...