Now to begin Book 2. Click here for a Book 2 Walkthrough. You should also begin trying to get into a Greater Barrows run. There are 5 quests here to complete. Each of these will net you some good gear as well as great experience.
You can also make your way to Ost Guruth in the Lonelands to continue through your Lonelands quests. Ost Guruth is located at 31.3S, 29.6W. If you work through some of the Fellowship quests during these levels you should easily hit 25 without having to travel to Trestlebridge. But if you are running a bit low you can begin a few quests at Trestlebridge in the Northdowns (head north out of Bree following the road).
Level 25 - 30:
At this point the Northdowns will be your primary home for awhile. You can complete quests in Trestlebridge, Amon Raith (12.6S, 52.8W), Meluinin (13.7S, 44.9W), Othrikar (6.9S, 44.9W) and Esteldin (9.7S, 42.1W). The Northdowns is full of quests and you shouldn't have a tough time completing most of them.
You should also complete Book 2 during your last few levels back in the Lonelands. When you complete this book a series of quests in the region of Agamaur will open up (29.7S, 27.3W). These quests lead to the instance of Garth Argawen, the second major instance for the game. There are a total of 9 quests to complete inside of this instance. I would begin these quests around level 32. It's tough inside of there, but there is great loot and experience to be made their.
You can begin Book 3 in the Northdowns during this time as well.