I'm looking for a word that describes shy and reserved, but not to portray weakness or one that has a negative connotation.
Being shy and reserved as an executive doesn't fit well for career opportunities.
Soft-spoken might be one alternative that puts reserved behavior in a more positive light.
I suggest the word quiet.
Susan Cain wrote a best-selling book entitled "Quiet – The Power of Introverts in a World That Can't Stop Talking," which I highly recommend. She contends, and I agree, that being seen as a quiet person is a good thing.
Here's a brief summary.
At least one-third of the people we know are introverts. They are the ones who prefer listening to speaking, reading to partying; who invent and create but prefer not to pitch their own ideas; who favor working on their own over brainstorming in teams. Although they are often labeled "quiet," it is to introverts we owe many of the great contributions to society – from Van Gogh's sunflowers to the invention of the personal computer.
Let me see. A word or an expression which will not lie about your character but rather shed a positive light.
A deep thinker
It depends on the context in which you plan to use and the syntax.
Quiet is described as being calm, gentle, and reserved. It is a positive trait. Naturally, when we meet the quiet people, we note that their dispositions and countenances are peaceful, serene as a light in the darkness. It is one of the greatest strengths and behaviors that a person can ever have because it weakens aggression and other negative traits.
Shy and reserved as adjectives aren't negative descriptors themselves. It's people's perception and our cultural perception of the "ideal" and traits of "value" that put the "ugly" into these words. So, until the current public acception of shy and reserved being undesirable characteristics, how about: Thoughtful, conscientious. or how about; awareness that the center of the universe is actually EXternal, not internally centered around you. Sometimes it's what we're NOT that makes us a valuable asset for someone. Supportive, not investigative. Accepting, not minutely critical. Observant, not fumbling winging-it fool! All these people that responded to your question acknowledge the many wonderful and valuable attributes that parallel being shy and reserved. Live strong introverts!!!