Col. Robert Venerables giveth instruction

This link goes to the entire fascimile edition of Venerable's 1662 work, "The experienced Angler, or, Angling Improved Being A general Discourse of Angling: Imparting many of the aptest wayes and choicest Experiments for the taking of most sorts of Fish in Pond or River."
This is a pretty killer volume, loaded with tips and verse.
Money Quote:

When you come first to the river in the morning, with your rod beat upon the bushes or boughs which hang overthe water, and by their falling upon the water you will see what sorts of flies are there in greatest numbers; if divers sorts, and equal in number, try them all, and you will quickly find which they most desire. Sometimes they change their fly; though not very usual, twice or thrice in one day; but ordinarily they do not seek another sort of fly till they have for some days even glutted themselves with a former kind, which is commonly when those flies die and go out. Directly contrary to our London gallants, who must have the first of every thing, when hardly to be got, but scorn the same when kindly ripe, healthful, common, and cheap; but the fish despise the first, and covet when plenty, and when that sort grow old and decay, and another cometh in plentifully, then they change; as if nature taught them, that every thing is best in its own proper season, and not so desirable when not kindly ripe, or when through long continuance it begins to lose its native worth and goodness.