How do I know when to use 'avoir' and when to use 'être' to form the past tense with a reflexive verb?

Most verbs take the auxiliary verb (think, the helper verb) 'avoir' to form their past tense.
E.g. 'penser' - j'ai pensé (I though, I have thought).
However there are a number of verbs that will use 'être' as the auxiliary verb. A lot of these verbs tend to be ones that are frequently used, and so it is essential to know which verbs take which auxiliary verb.
The first type of verb which takes être is a reflexive verb. There are no exceptions to this rule. When you want to use a reflexive verb in the past, its auxilary verb will always be être. Let's take for example the verb 'se habiller' (to get dressed):
Je me suis habillé. (I got dressed).
In contrast, if we use the non-reflexive verb 'habiller' (to dress someone or something else). We will use the auxiliary verb 'avoir'
J'ai habillé ma fille. (I dressed my daughter).
As you can see, the use of avoir or être as the auxiliary verb is dependent on whether the verb is used reflexively (dressing yourself) or non-reflexively (dressing someone else).