That means they're reading you because you're predictable. Make yourself less predictable. Get in range for a side+B or paralyzer like you normally would, but refrain from using ANY moves. You must wait for them to react to you and then punish them. Bait them to attack you, attempt to dodge or shield their own attacks. If you get in range for melee attacks and they still haven't acted, harass them with jab cancels, dash attack to up-tilt (so you cross them up), and other things that they cannot easily spot dodge and punish. Be careful about harassing them with the dash attack to up-tilt, as they can probably punish you if you use it too much (shuttle loop from shield is probably something they could do, or jump cancel to aerial), but it's an option that you could get away with every now and then.
The trick is baiting them into acting and punishing. Brawl favors defensive play over offensive play, but the real trick is to learn how to meld defensive play into an offense. It really comes down to who can read and bait their opponent better, once you get past counter match situations.