Don't speak loudly or interrupt others when you state your opinion. Speak calmly and give research for your opinion. Don't deliberately start a conversation that you know will turn argumentative.
Being assertive is not in itself trouble making, but if "speaking your mind" means you want to say hurtful or aggressive things to others, you may want to run this by someone you trust first to see whether your assertiveness crosses a line.
First of all,when asserting an opinion, you have to consider other people's feelings, taking their perspective on the same issue. Second, always respect others' perspectives, do not think that you are the only right person.
