If believe people aren't taking you seriously, they won't take you seriously.
Though if you believe people are taking you seriously (with all your heart), they will take you seriously. A lot of this is non verbal stuff, I mean I could tell you a whole load of tricks for people to respect you and be amicable, but believing that what you are saying is worthwhile with all your heart will instantly transform your non-verbal to a good state. And you will be made if people don't take you seriously, because what you are saying is important, why aren't they taking it seriously! (Once you get mad with someone for not taking you seriously, they will usually take you seriously :P )
I think what you are experiencing is a self esteem thing and not a SA thing.
Thank you, but I'm pretty used to my family not taking me seriously. I've been mad, been stern, been serious as could be and it doesn't help. But thank you for the tip.
As for strangers, they generally take me seriously enough. I'm not worried about them.