About this particular case, you can leave the second subjunctive out:
"Era importante que adulara ... si quería ...".
si is used only when the situation is unlikely, and in that case the
si part almost always starts the sentence. Also, you "step back" a tense, so, if you are talking about now, you use the imperfect:
Si quisiera [now] buenas notas ...
but if you are talking about something that happened in the past (as in your case) you use the pluperfect:
Si hubiera querido [at that time] buenas notas ...
But, as I said, you usually just use the indicative.
In the general case, when you have two or more subjunctives, you should think about each of them separately. It doesn't matter whether the other part of the sentence is in the indicative or subjunctive mood; they don't "add up" or something.
For example, if you want to say...
Para que me diera buenas notas era importante que yo notara que él esperaba que yo lo adulase.
...you can make the decision about the mood of each verb without looking at the mood of the others. I.e., adular would be in the subjunctive regardless of the mood of esperar, and so on.