Whilst not at all experienced enough in this game to beg authorship of a guide, I have played a good share of factions thus far, and my only successful campaign was in command of these fine peoples!

They have access to strong, blitzing light-infantry like the Vikings, and javelinmen - Novgorod melds Scandinavian influence with Nomadic steppe culture in her unit selection.
Boyars, Horse archers and Mounted crossbowmen are available early, as are Druzhina Infantry and Cavalry, and Russian Spearmen.

Novgorod has a powerful selection, and a diverse selection in the early game, and I have found this power only to be matched by Novgorod's primary rival to the South-East, Kiev.

In my own game, I allied with Kiev, but I was forced to due to a critical mistake.

The Principality has almost immediate access, through conquest, to five seaside provinces, and thus has the potential for great naval power which I myself utilised.

However, it is quite crucial to ensure that you have Muscovy, Chernigov and most of the East under control within the early game.
Even if this means warring with Kiev, in the early game, Lithuania will be too interested in Scandinavia, Norway, Sweden and Volga-Bulgaria too poor, and other factions too far away to consider attacking you from behind whilst you conquer the East.

In my game, I made this mistake, and conquered Finland, Estonia, Livonia, Smolensk and Lithuania.
However I ignored Muscovy briefly, and soon found myself on a long, heavily guarded border with a neccessary ally - Kiev.

By the time I was powerful enough to strike at Kiev, my attention was needed elsewhere due to growing Catholic threats.
And so, even though I was generating thousands of florins from all of my provinces, (With such good trade), I was stalemated by my reluctance to expand east in the early game, which would of allowed me to relinquish my garrison in Novgorod - and have a standing army.

So in my game I became a huge naval power, (Longboats are pitifully cheap!), and conquered small places like Scotland and Ireland, Corsica and Rhodes.
But I was too far behind the West, and could not fight the East for fear of the Catholics, and the dangerous web of trusting alliances.

It was a peaceful game, and although at home I had few provinces, and only garrisons, (Of 700 men each), I was respected by even the greatest Empire, the Danes, who conquered half the known world.

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You may be able to derive from this, and the detail it shows, that I truly loved my game as the Novgorods, and I think - due to a length of playing it in a peaceful manner - the only fault that will lead to the collapse of the Principality is being too nervous with your fellow Russians in the beginning.

The Principality is recommended for a challenging and varied game against all religions and several different factions in-game, and an opportunity for naval conquest.