When expressing your opinion,
1) Mind the tone of your voice.
  -It can be disrespectful to some because of the way you said it.
2) Use the phrase "in my opinion.."
  -to avoid any other confusion and to clarify that what you said is by perspective or by any other means.
3) Be open-minded
  -people won't respect you deserve if you don't give them the respect they deserve.

(Sorry, this is more like a how-to..)