To Look Lean, Forget The Machines
A gym instructor, who tells you to stay away from the machines, will have to look for another job soon. Which is why gyms are museums of some pretty useless high tech machines. There's nothing a good sprint, or good home workout that comprises of pull ups, squats and push ups can't take care off. In fact to build lean muscle mass, and get strong, bodyweights are more crucial than heavy isolated weight workouts.
Mix It Up
In all probability your gym trainer asks you to follow a set list of workouts for 6 days of the week. And their horror when you break the rules and mix it up, knows no bounds. Try it and we guarantee you will have 3 instructors at the very least swarming around and trying to talk you out of the madness. But mixing it up, trying new things, and randomizing workouts is very important for weight loss, not to mention, to fight boredom.
Take Cardio Outside
While most gyms instruct you to come 6 times a week and run on the treadmill alternating between weights and cardio, not too many will tell you to try other forms of cardio outside of the gym. But do try running outside, cycling to new destinations, or taking up a high intensity cardio sport. This not only ups your intensity but simulates do or die situations, which prompt you to work harder than you would inside a gym.
Look Outside Of The Gym
An instructor who tells you this most certainly doesn't want to work there for much longer. But with all the various fitness trends doing the rounds like power yoga, body combat, zumba, etc. do you really need the gym? If you are enjoying it, continue by all means, but if you are bored or fatigued with the same routine, it's time to step out.
Don't Spend Hours At The Gym
It's best to go, finish a routine of some heavy weights, do some functional movements, and leave. Instead of spending hours doing isolation exercises, if you can finish your workout in 45 minutes working out the core and the full body, you can have a complete workout that will leave you regenerated instead of ruined.