Came across this list of 17 ways to be more productive at the gym.
It all makes quite logical sense, incorporating ideas like progressive overload, good hydration, and knowing what you are trying to achieve. Being in a gym you're surrounded by a bewildering array of machines and equipment. Having a plan is really helpful.
Of course your gym induction, assuming you got one, will have set out a basic plan, but if you're still doing the same thing after 6 months, then it's time to revise your plan or get someone to do it for you. I have my plan in my head, but a better idea is to write out a few plans on index cards and carry them in your bag. That way you can pick a routine and do it.
If you don't know about things like FITT principles, then you should do a bit of research. It will help you develop your understanding of how to get the most out of your fitness routine.
And lastly, you can take all these principles and apply them to exercise outdoors. or even at home. You can do a very effective exercise routine in your lounge with just a chair, a resistance band and a bit of creativity. I wrote a blog post about a simple 8 exercise circuit that can be done really easily with no expensive resistance machines required. Add a bit of cardio by going for a walk and you've saved yourself the cost of a gym membership if that's what's getting in the way.