Recently one of my students asked me to teach him openings. His strength is around 1300 Elo so I asked him if it isn’t more to improve his basic chess skills at this stage after which you can play against any kind of opening using general principles. But I think he might not like my advice. I have observed a similar attitude with many amateur players; rather than focusing on strengthening essential skills they are spending hours and hours on preparing chess openings.
In a similar way to how every chess position offers something, this situation also presents a wonderful tool for enhancing a student’s knowledge. The tool is to change their openings periodically. How this will help in improving? I have discussed it below.
You can use one opening ideas in another one: for example, playing caro-kann opening as a Black and d4 as white. You would able to find many similarity in both where you can use one opening ideas into another one. If you are playing QGD exchange variation, you won’t be having any problem in finding plans while playing exchange variation caro-kann (Playing as Black). You can find lots of similarities when you play against tarrasch defence and defending against panov attack.
Learning different kinds of pawn structures and related strategies: You can learn different kind pawn structures by playing variety of openings. For example, Panov attack helps in learning to play with isolated pawn structure, French two knight variation (As white) helps in learning to fight against hanging pawns. QGD exchange variation helps a lot in learning minority attacks.
You can add some more points also but above are the one which attract me to go for this kind of teaching method.
You can choose basket of openings for your students after doing his strength and weakness analysis periodically. This is kind of vice –versa that in order to develop a particular skill you should play some selected positions and to play those positions you required some skills. By this way you are developing skills through the experience and dreaming that actually you are preparing openings.