To imitate the nymph of any baetis, my number one pattern is Oliver Edwards excellent Baetis Nymph. To look at the fly it appears complicated; the individual processes used to make the fly are simply enough and once you've learnt the "route" you can tie them reasonably quickly, but they are by no means a five minute fly. Sizes 16-20 will cover all of the common species, all you'll have to change is the colour.
The next stage to imitate is the emerger. I don't have many emerger patterns and one that I've recently tied is a variant of the Cul-de-Canon. This is a pleasantly quick tie along with being a simple pattern; I feel the addition of a squirrel thorax enhances the suggestiveness.
Once the emerging fly has hatched into the dun I won't hesitate to tie on my Barbour Paradun. An amalgamation and rip off of two Peter Hayes patterns. I have taken the shape of the PhD and combined it with the silk thread body soaked in liquid wax of the Muskrax.
I'll also have a few PhD's tucked away if needed; this style of fly is very versatile and will even imitate large mayflies if tied in the appropriate colours.
If the trout won't take a hackled fly then a sure fire bet is the JT Olive.