If you want to see results, any trainer will tell you, you need to push yourself out of your "comfort zone." If you do the same thing every day, at the same level, can you really expect yourself to improve? I don't think so.
Over the last 6 months or so I've had the opportunity (alhamdulillah) to work with a personal trainer. In that time, I've seen my energy skyrocket, my entire body enhance its muscle tone, and I've even lost weight. It didn't happen sitting in a chair, and it didn't happen just by going to the gym.
Lifting a weight won't necessarily make you stronger. If it's a light weight, and is easy to lift, then you're not improving or developing your strength to lift it. And even if it's heavy, just lifting it once doesn't do much to improve your strength either. But if you want to get stronger, you have to take the hard route, and push yourself as far as you can, repeatedly. Ideally, to failure, again and again.
It's the opposite of the "If at first you don't succeed..." mantra. The goal is in fact to push yourself to the limit, i.e., to failure. And when you can't lift any more, you've pushed yourself out of your "comfort zone" and you know that you're getting stronger. (Provided of course you didn't actually injure yourself and that's the source of pain and reason you can't lift anymore... and that's very bad.) And if every week you go in and perform the same exercise, with the same intensity, and for the same amount of time, eventually you're going to stop getting results. You have to actually increase the intensity or time to see further improvements.
I know it might sound weird, but how about applying this concept to ibaadah? (worship) Instead of just performing our acts of worship (like salah, for instance) the same way all the time, why don't we push ourselves to do them better? With more sincerity, with more khushoo'. We have to move out of our "comfort zone." Now, a comfort zone for each person might be something different, and we might have different things to work on. We can't expect to just immediately have more khushoo' in our prayers, can we, without making an effort to have more khushoo'? Without making a conscious effort to improve our khushoo'?
I guess if we feel like we're in a rut with our ibaadah, then we should make a conscious effort to improve upon our weaknesses. That means, get out of the "comfort zone." And don't keep doing the same thing expecting improvement, without holding ourselves to a higher standard. A good tip might be, for example, to create a Khushoo' chart, or a chart for whatever it is you're trying to improve. List all the prayers out and give yourself a rating for each prayer on your chart, like a rating for khushoo' on a scale (like 1-10.)
I'm not sure it's even possible to get better without making a conscious effort towards improvement. And one thing about improvement--once achieved, there's motivation to keep it up and continue to avoid backsliding. Just some thoughts...