I used to get this but somehow got over it. I now always walk briskly and positively and immediately stamp out any stupid self-concious thoughts when they enter my head. If I have to walk past a queue of people, (eg bus-stop), I just look down at the ground ahead of me and walk briskly past without even thinking about engaging in eye-contact. People might be looking at me as I walk past and it would be very easy for me to get self-concious and nervous, but rather than let it worry me I just say to myself "hey, screw them, I'm not even going to acknowledge their existence by lifting my head to look".
A large number (if not all) people with SA have problems with self-esteem, thinking that they are less worthy than others and that others will be negatively judging their every move. The trick is to just treat strangers like they're doing you harm - so if you worry that they're going to be laughing at the way you walk, just say to yourself that these bunch of fckers can kiss my beautiful ass - I owe tham nothing and can walk whatever way I bloody well want...how dare they criticise me!! Sometimes it's good to get a wee bit of anger in your mind to help reduce the feelings of unworthiness. Avoid the eye-contact too as if it just so happens that someone is looking at you, it may make you get a sudden feeling of self-conciousness, so just decide that you're not even going to lift your head as they're not worthy of your attention.