You can try for E+ either at check-in (by requesting an exit row, usually) or at the gate. UA is starting to be more strict about just giving E+ away since it's a moneymaker for them--either in loyalty as a reward for FFers, the purchase price of the higher Y fares, or the payment when offered at Easy Checkin machines.

Your best bets are to (a) pay up to an upgradeable fare, which often isn't really that much, and try to get a SWU from Coupon Connection; (b) if Mr. Chicken offers an E+ or other upgrade for $$$ at check-in, take it; (c) pray for an op-up (the latter being not bloody likely!)