I have some that I'll jot down, but before I do, a point. Having a personal tutor who used to mark for a well known exam board, if you're using the imperfect subjunctive, STICK TO THE SAME ENDING.
If you use "tuviese" then "fuera" then "limpiara" and say "tuviera" again, it shows you are simply remembering phrases. By sticking to the same ending you are showing the examiner that you are aware of the conjugation of the imperfect subjunctive. I personally use "se" for it as it seems to roll from the tongue better, but "ara" is fine too.
And for some phrases...
Me da la impresión de que - I have the impression that
Estoy de acuerdo/a - I agree..
Es probable/una lástima/vergonzoso/discutible que + SUBJUNCTIVE - Its probable/a shame/shameful/debatable (use with subj. as doubt exists for some and they are imprsonal expressions)
Pensándolo bien, creo que - On further consideration I think that
Pensándolo bien, NO CREO QUE + subjunctive - On further considerion, I do not think that...
Ya que - Because/given that
Tampoco - neither (use instead of "o" as o can be repetitive)
Si yo fuese ellos/la gente/tú + imp subjunctive - If I was them/the people/you
Structure markers, e.g primeramente, para concluir, para empezar all help boost your mark where there is a mark for quality of response.