You don’t have to add “avant ” every time, if you just use the “imparfait” tense, it will be enough in most situations. If needed, you can add an adverb to make your statement clearer, but it is not mandatory, the verb alone in the the imparfait will make sense and is certainly not a mistake.

You can also use the phrase “avoir l’habitude de” if you are talking about a habit:
He used to ride the bike : il avait l’habitude de prendre le vélo.

BUT you would not say “il avait l’habitude d’aimer cette chanson”: this is not a repeated habit but a permanent state.

The idea of “… used to …, but…” can be expressed clearly with the phrase “à l’époque / au debut” followed by “mais aujourd’hui”:

e.g.: Ça me semblait trop éreintant pour mes pauvres petites jambes, à l’époque / au debut. Mais aujourd’hui, je m’y suis fait.

Another example:

Nous y nagions autrefois. {= We used to swim there.}

Just as in the 1st example, Imparfait is the correct tense to go for. And again, the addition of an adverb such as “autrefois” helps to make it clearer that whatever used to be the case back then is no longer so.

The famous phrase “Longtemps je me suis couché de bonne heure” (M. Proust) is usually translated in English as “I used to go to bed early”.

An overly formal way could be

Il fût un temps où …

Again, this is certainly not what you would use in a normal conversation but in a specific context (formal, sarcastic, …) it could be a good fit.

“Il fût un temps où ..” is indeed a very elegant way of expression the idea of “used to”. It’s slightly formal, but it can be heard in polite and educated cercles of French speakers. It also exemplifies the idiosyncratic usage of the adverb “où” (where) instead of the more logical “quand” (when). Another less formal way to express the idea of “used to” is by using the adverb “a une époque”:

A une époque, je fréquentais un cercle d’amis qui … ( [A while ago] I used to hang out with a group of people who …)