The difference between climbing with good technique and climbing with bad technique is night and day. Someone who knows exactly how to efficiently exert themselves can last hours longer than someone who has no idea how to climb at all. There are several key ideas that make a climber a good climber and those are conserving strength, moving efficiently and thinking
critically. All 3 of these are skills that take a long time to master, but drastically affect the performance of a climber.
When you start off on a route, you need to first look it over. Take a minute or two and plan how you think you should climb it. Think of a handful of different ways to tackle it before giving it a go and tuckering yourself out. Every route on the face of this earth has more than one way to finish it, although some much better than others.
Once you have decided how to go at it, try to stay in positions where your arms are extended or your body is all the way up to the wall if you can. Both of these positions use much less physical energy and can help you maintain climbing endurance. Staying in positions of constantly flexing or stressed muscle will zap all the energy right out of you.
Also remember that your legs are some of your best tools. Thigh muscles are incredibly strong- so much stronger than any muscles in your arm- so remember to utilize them as often as possible. Climbing with your arms can be fatiguing.
Following these steps is a great way to start you on your journey to becoming a great climber.