Coming anxiously out of the Lone-Lands you are slowly introduced into this new found land. A burned house stands right before you, smoke and fog everywhere; it is a place that already feels like trouble and that seems to be only the beginning. The North Downs for me stands firmly as one of the most key regions of the game where you are most likely to spend your life from level 20 to level 40. You have about 250 quests to choose from, the Fornost instance to explore and several deeds to complete however it is most crucial for you to organize yourself to gain your experience wisely, and fast. I will try to outline some of the essential areas that you must take advantage off and especially some of the best rewarding quests which will provide you with a wealth of experience and items.
Trestlebridge itself, alongside Greenway, has a few useful quests that lead to the Nan Wathren area to the East. It is of utmost importance for you to take notice of it and form some solid fellowships in order to kill your way through the elites. Half-Orc Schemer (level 28) and Vile Poison (level 24) both base themselves in the depths of Lugbas' territory which is prime land for gaining some experience. Later on when reaching Esteldin you will be sent back to Trestlebridge with A guardian's duty (level 30) and A promise fulfilled (level 29) both yielding some nice selectable rewards for a number of classes. A final encounter with this region will most likely be the Defence of Trestlebridge instance at level 30; an easy quest to do with not much of a requirement on the fellowship set up. Moving on you will be traveling north towards the Fields of Fornost and Amon Raith. At this point I am not moving in any way by the level of the quests but by the way players usually carry themselves in this environment. Being new to a region usually leads in following the main road and breaking off whenever a quest area is found.
The Fields of Fornost have two main quests you must not omit; Ending the Elder (level 35) and Seeking the Source (level 35). The area itself, besides Fornost to the north, is fairly barren and you will most likely go through it pretty quickly. Amon Raith on the other hand has one of the most essential quests in the North Downs, and that is A collar for a King (level 36). This will require you to enter the Fornost instance to the north of the fields yet the level will probably not get you through all the way to Krithmog so it is better to wait until level 40 or more, after which find a solid fellowship with a great healer and some sort of invincible tank to batter through the hundreds of elite mobs. The Scout Becomes the Hunter (level 22) is another excellent choice to do earlier on especially if you are looking for some useful gear.
Moving more towards the east and into Annundir and Kingsfell you will find a zone lacking in content without much quests to choose from. If you are desperate for work you might be able to find something at Gatson's farm, if not move either north to Othrikar or keep going east towards Esteldin. Othrikar is more of a late 20s early 30s city and there are a few things to consider while on your visit there. Birds of a Feather (level 24), Meat for the Hungry (level 30), Pulling Beards (level 30) as well as the Father-Lode (level 29) are some handsome rewarding choices for you to take advantage of. You will also have your first introduction into Nan Amlug West as well as the East, a region which you will later be feasting in with the finding of Esteldin and deed requirements.
The city of Esteldin is in my view the capital of the North Downs. With an astonishing number of about 90 quests either starting or involving it at some point in your journey to level 60, Esteldin's quests reach into three other main regions of the North Downs; Nan Amlug East, Dol Dinen and Meluinen. While residing there you will come across a number of chain quests that are mandatory to consider. A leader unveiled (level 34), Leathery Wings of the Drakes (level 33), Mother of the Valley (level 33), Reclamation (level 30), and Plague Bearer of the North (level 36) are some fine missions to follow in order to familiarize yourself with the area as well as increasing your level in preparation for Dol Dinen down south. It is vital to go into Dol Dinen well equipped and in a strong fellowship if you want to finish all the designated quests. I have struggled many times either because the monsters were spawning too fast for the group to advance or some of the members were not paying attention and grabbing agro left and right. Once you enter the area you will see everything is bottlenecked and tightly structured; moving around solo away from your group is generally not a good idea.
The region is not to be missed since Orcs of the Blood Mountain (level 32) and Siege-Master (level 35) will take you in the middle of the elite frenzy with some rewards to come out of it. There are many other quests to consider pairing up also yet that depends on how willing you are to revisit the area and if the right fellowship comes about. Meluinen, which is to the west of Dol Dinen, also puts out some content worthy of taking into account. Respectively, Tending the Glade (level 28) and The Troll-Keeper (level 33) which could provide some use especially if you are willing to put the time and effort in getting as much from this region as possible.
Lastly I would like to skim across the Fornost instance a bit to give some idea of what to expect and how prepared you have to be. I will not enumerate the quests however The People's Camp to the south-west of the Fornost entrance offer a great deal and will come in handy especially for the experience. The instance in itself is sufficiently long to have some of the fellowship members leave half way. And by half way I mean when you reached Rhavameldir; the following section being much more difficult than the first. It is important to take Fornost in consideration as you will get a lot of out it, both items and levels, however to reach Krithmog you will most likely need a fellowship over level 40 in order to succeed in a reasonable time. I have seen some nice drops even from the early bosses such as Warchief Burzgash (Tugharn Helmet) but also from the later Elite Masters such as Brogadan (West Gate Key, Daerchar earring, Ruingurth dagger and the Narcham legs). Bottom line is, put in the time and you shall be rewarded. Deeds will generally come out of the quests themselves, and if not I generally found that I did not need to put any extra substantial effort in grinding for them as I had for other regions.