Hi Kar Yan,
Good day. As I am reading your question over and again, I guess the advice/suggestion that you are looking for is how to 'constantly feel uncomfortable'.
Maybe let's set a common understanding of the term 'comfort zone', then we'll see if we are agreeable on our context and understanding. That will decide how relatable my following advice will be working for you.
Comfort zone is a state when one feels at ease. There is nothing new, there is no challenge, there is no growth, and one is just being completely stagnant in his or her work.
So, to be 'uncomfortable', or even being 'constantly feel uncomfortable' is to drive oneself to be hungry for change; change to be better, to do things differently, to achieve higher. There are many ways we can do to get out of the comfort zone but often enough we sink at a guilty point where we got comfortable and forget to challenge/improve ourselves. (Mike in his earlier answers gave some really powerful advice on 'how to' go out from that comfort zone.) So constantly reminding ourselves to 'get out' is necessary and here are some of the tips that I have been practising, I hope it will help:
1. Boring is your best trigger:
No matter what is your given assignment, task, or role, there should always be an excitement factor. You know you are learning something new. You know you are now doing it a little differently than before. You know there are routine was improved in some ways.
When you no longer feel it that way and feel bored on the routine that is unchanged, you know you need to start looking out.
2. Plan your day and plan your days ahead:
Every morning, try to give yourself time, maybe just a short 5 minutes to review how your day is going to be. Is this going to 'just another day'? If it is, then what can you do differently than how it has always been done?
At the beginning of every month (or a specific timeline), look at what has been done for the last month (previous period), and what can be done better or more this month (coming period).
3. Ask the 'how would [someone] do it?' question:
Remind yourself of your role model. He or she can be a famous person, a mentor, a successful figure around you, or just your superior.
From there, have a habit of asking yourself, 'if this task is given to him/her, how would he/she do it'?
To make it better, if you can't think of an answer, you could even discuss this question with someone or that person him/herself to inspire your thought process.
Lastly, as a generic rule, be ambitious but start small. I always go with a rule of 3. That make things practical. You'll hear from a lot of people on tips and tricks on stuff. Keep to yourself 3 that you know you will be committed to, then work from there. Being greedy in this sense will cause you to lose focus on your goal and defeat the purpose of why you get started.
I hope this help answers your doubt. Feel free to get in touch.