Basic human psychology is such that one negative experience often outweighs up to 7-8 positive experiences - and that one negative experience is remembered over those positive experiences.
Obviously, that has HUGE ramifications for those who struggle to fit in to a group, but it also has direct impact on how we should be commenting in church.
If we say something negative or contrary more than about 15% of the time, we will be viewed by many as a complainer - and what we say will be tuned out eventually or used as evidence that our position is just one that grumpy jerks take. Therefore, it is critical that the strong majority of things we say be positive and reinforcing.
Basic psychology also dictates that tone is every bit as important as content. Simply put, if my voice indicates superiority or condescension or anger, my words often will taken as negative - even if they really aren't. On the other hand, if my voice is calm and gentle and softly spoken, people naturally will not feel like they are being criticized or attacked - even if my words challenge what they have said. Sometimes, it's important to make a challenge an obvious challenge, but I probably can count on both hands the times I've felt I needed to challenge something forcefully and bluntly in church over the last 25 years.
With that in mind, here are some suggestions:
1) Pick you battles carefully and sparingly. Not everything has to be challenged right away - or at all. If someone perpetuates former racist justifications for the Priesthood ban, I'm going to challenge that - but . . .
2) Address the words, not the person - and avoid characterizations that label either. Keep it concise and on point. Don't say, "That's stupid" - or anything like that phrasing. In the Priesthood ban case, I might say something like, "I like what Elder Holland said in the PBS documentary - that he never understood the reason for the ban, but that the key is not perpetuating the former justifications for it."
3) Reference current apostles and Prophets whenever possible. With regard to the ban, you might add something like, "I have a friend [me] who has compiled a list of quotes from current and recent apostles and prophets about that question, and they all agree that the former explanations shouldn't be repeated." Generically, it really helps to be able to say, "I love what Elder Wirthlin said in his talk 'Concern for the One' . . ." - or something similar.
4) Don't be or sound counter-dogmatic. Frame your comments in terms of thoughtful consideration or wonder. "I've really struggled to understand this, and it's helped me to consider . . ." or "I wonder . . ." or "Someone I really respect used to say . . ." or "I know members who have found great peace by . . ." or anything else that doesn't come across as an attempt to challenge and convert. Reflection works well; opposition, not so much.
5) Be active in your local congregation. Whatever issues you might have outside the meetinghouse, fellowship regularly within the walls of the meetinghouse. Due to our financial constraints right now, we generally only travel to our meetinghouse twice each week (Sunday for Sacrament Meeting and Wednesday night for youth activities). We don't participate in all the other activities that occur throughout the week, including things like the Christmas dinner or another popular activity that just happened. However, we are there every Sunday and Wednesday - so everyone sees us as "faithful attendees". MUCH more latitude is given those with whom people associate regularly than those who show up only occasionally - largely because that gives you the chance to contribute positively enough to overcome the times when you feel compelled to challenge something.
6) Serve others. People will accept lots more things people say who are known as active helpers than they will from people who rarely, if ever, reach out and love them proactively and in deed.
7) Finally, be gentle, merciful, meek and non-judgmental. That generally takes conscious effort, but it is the ultimate key, imo. More often than not, it's not what you say but rather who people believe you are that is the biggest determining factor in if your words will be accepted.