You best bet is to meet other people who are questing in the same area as you in Marleybone. Make some friends and do the quests together, plus you will have some players to help if you get stuck in a street battle or when you need help with a boss. You should also check your equipment and see if you can upgrade it at the bazaar. Get an athame and ring with high health. If you need any shields you can also buy treasure cards.
Most players think MB is a tough world, and it is when you are at that level but by the time you finish big ben things will start to turn in your favor.
If you get need help with the Dungeons wait outside the entrance for other players with the same quest so you can go in a group of 3 or 4. You can switch realms to find a crowded realm where there may be more players.
If you play off hours or just get stuck you can go to wizard101central.com and post in the "In game Quest help and meet ups thread."