Fly by trim/ stick position. Particularly in a single seat glider where there's not much variation in CG. Trim sets speed (hands off stick). Find stall trim/stick pos, trim a bit forwards. That'll give you a rough approach speed. Better still, make a note of your trim position at approach speed when the ASI *is* working, even mark it. Let go of the stick it'll settle to that speed. If you let go and it noses down, too slow, etc. Wind noise is a biggie in a glider - I know I had to do circuits with the ASI covered and Alt covered before being let lose.. though that's easier in a draughty old K13.. Opening vents or the dv panel will make more noise and might help.
Same would also work with a powered a/c. Trim sets the airspeed, power will determine whether you climb or descend at that airspeed. I wouldn't be so confident doing it in a powered aircraft though, and messing with flaps and gear will corrupt that.
For my part I can't remember that many mnemonics, but I do remember how the pressure instruments work. A couple of minutes thought will tell you what it's going to do. Total failure is far less trouble than a more subtle one - The big problem is figuring it's giving bad data when it hasn't actually ceased completely. For instance flying partial panel knowing the AH has failed you still look at the d*mn thing. A postit is very handy to cover something that's misbehaving - a good visual reminder to ignore the bad data
