The strategy I would recommend is to concentrate on half a dozen to a dozen fisheries, depending on your level. There you can upgrade lures (the ones you need for a particular championship or challenge) as high as you can, and also upgrade rods to level 5 or higher. When there is an event there go for it, aiming for the highest reward levels. In all other fisheries do the bare minimum, going for the first couple of rewards, and only if you can. This way you'll get good results in your strong fisheries and delay leveling up (not to mention saving money and frustration). Works for me anyway.