If you've not had luck in the past, I suggest not trying again. Why continue to kill animals?
I'm on my second (lost my first due to an extended power outtage a couple years ago). My first was an assie that did very well, my current one is cultured and coming around nicely (had it about 2 months, was in so-so shape when I got it.
I agree with the advice above... if you insist on trying one again, good, stable water params, moderate light and moderate flow.