If you want to see progress from your training, particularly in the form of increased muscle strength, it comes down to one thing - pushing yourself past your comfort level.
If you're not reaching a point where you are struggling to lift that last rep or run that extra 100 yards or hold that pose for a final few seconds, then your body won't change. It has no reason to if its working within its capacity. You have to overload it, do something that shocks the system. If you're not giving your muscles more stress than they are currently built for, they have no reason to change. Our bodies change only when they need to, i.e. when they're exposed to a stress that they must adapt to.
My absolute favorite quote I live my life by - "Sacrifice what you are for what you want to become". Seek out the struggle, you'll thank yourself for it later.