"remember also, that certain things take certain other things before that thing can be built. for instance, getting more ships isnt just a matter of increasing the priority for ship building; you also have to make it easier for the ai to build merchants, ports and shipyards, as well as the ships themselves."

Kraellin is right on target with this observation. Not only does increasing the numbers increase the AI build preference, but in addition, you must remember that the probability of getting the AI to build any particular unit is also dependent upon a number of different factors, such as what AI behaviour is currently being utilized. If the AI behavior shifts to close_to_support_limit then it's not going to build many new units, but will increase the probability of building merchants, for example. Also, you will not that the AI tries to build balanced armies, with a predominance of line infantry/spear units, so the probability of building any particular (say cavalry) unit at any given time would also depend upon what units were present in the province.

That said, probably the most successful way I've seen to influence AI behavior is to increase the AI income, either by increasing the province income or providing additional resources or both, plus increasing the AI build preferrences for shipyards, shipbuilding, and merchants. This will increase the production of all unit types. Kraellin, +DOC+, myself and others have all done that with some success. Kraellin's Early Russia Q mod is a good example, downloadable from this site and you should take a look at it.

Even with all that, depending upon the AI start behavior it may not respond as you would wish. I experienced great frustration getting the Byzantines to expand a trade network, until I realized that I had set them to Orthodox_Defensive. Defensive behaviour sets tend to make the AI use it's shipping defensively to block invasion routes, rather than build its trade empire.