(I have deliberately limited this to one page; there is one page of overall advice, as well. LEP)
Every color in Britannia must be played as a whole, not as separate nations, if you want to win consistently. Sometimes it is worth sacrificing armies or points of one nation to improve the points or position of another by a greater amount. The action of armies at one end of the board can affect those at the other, in the long run. Remember, at a given time position is just as important as the number of armies or number of points scored so far.
Yellow always appears to be in the lead early in the game, because the Romans score so much. The Yellow player must convince others that the Romans "must" score a lot to give Yellow a chance. Some players may go so far as to "play possum", scoring less early in the game in order to appear to be "not the leader". Others try to "lead from the front", as one player put it, ultimately getting a sufficiently large lead thanks to Scots and Dubliners (and maybe Romano-British) that nothing can be done to pull the Yellow back late in the game (when the Norwegians can usually score a consistent amount, especially if the Dubliners have done well).
Yellow does not want a game where everyone scores fairly high, because a very high Yellow score is difficult if not impossible to achieve. Red and Blue have many more chances for high scores. So Yellow must try to keep Red or Blue from dominating the board.
Yellow is odd to play because it has a "Big Bang" at the start, a smaller Bang at the end, and a lot of being careful in the middle. Two Yellow nations are among the lowest scorers in the game. The Romans dominate the game, then disappear. The main objective of the Romano-British is to survive for a while. Sometimes the Scots struggle for survival, sometimes they can do quite well and control several areas at the end of the game. The Dubliners can dominate the middle of the board or disappear, depending on many circumstances, but they donít score much. Norwegians have a fairly certain score in Round 15, then a lot of uncertainty.
Barring quite bad luck, the Romans usually score maximum points (80) at the end of Round 3, given reasonable play by other players. If others are unreasonably intransigent, Romans may score less, but the defenders will hurt for the rest of the game. The Yellow player needs to convince Roman opponents to submit, possibly by offering them full population growth.
Any Roman who doesnít take Devon in his first move, or doesnít take Downlands before the Belgae submit, has Screwed Up Bigtime. Devon is needed to make it easy to force Welsh submission in the first Round. Downlands in the hands of the Belgae revolt is poison, as it can reach so many areas that defense will be weak. The preferred situation is for the Romans to have at least two and perhaps three armies and a fort in each area the Belgae can attack. If the Romans force Welsh submission, they can redeploy their armies to achieve this "Maginot Line" defense against the Belgae.
Thanks to the Roads, the Romans donít need to risk lots of 1-1 attacks to achieve their objectives. But 1-1 is pretty good odds, even so.
Scots can usually get Dalriada and Skye. They may have to wait until Fergus appears and come ashore "en masse", rather than come piecemeal. Some accommodation can often be reached with the Picts. Yellow does not want to get into a long battle with Blue in the north, if possible. It is very rare, but I have seen Yellow with no pieces on the board for more than one turn because the Scots got into too many fights.
Dubliners are quite variable, and have many options, such as helping pave the way for the Norwegians. There are multiple routes to the big points in York. Norwegians should get near maximum points on Round 15. Often Harald will be killed in Round 16Ėthere are just too many enemies, especially with the Danish king coming in Round 16.