This is a route I take regularly as I live local so listen carefully and you will get there no probs:
1. Arrive at Euston and go to the underground and take the NORTHERN LINE SOUTHBOUND (if memory serves me correct you want PLATFORM 6).
2. Get off at BANK STATION (takes about 10-15 mins) and as you get off look for signs for the DLR on the wall opposite you with arrows pointing towards the middle of the platform. Go down the stairs and at the bottom turn LEFT onto the DLR Platform.
3. Destinations from BANK DLR will normally be LEWISHAM (Don't Get These Ones) and KING GEORGE V (Jump On This One). You wont have to wait more than 10 mins usually before your train arrives.
4. After 7 stops (about 10-15 mins), get off at CANNING TOWN and STAY ON THE SAME PLATFORM for a train going towards BECKTON and get on it.
5. After 2 stops (about 3-5 mins) get off at CUSTOM HOUSE and welcome to the Excel Centre!, just walk up the stairs at the end of the platform and turn right
If you want you can contact me via email (in Trust) n should you want more details you can also take my mobby number in case you get lost.
**EDIT** Total travelling time about 45 mins depending on amount of time you have to wait on the platforms for the appropriate trains.
**EDIT2** There are disabled facilities (IE lifts etc at all DLR Stops) and the only stairs you would have to navigate are from the BANK platform down to the DLR platform. Apart from them the rest should be all escalators and lifts
