Don't worry about playing high ranked players, they are predictable. It's the newbies that are dangerous.
Anything you do can get you attacked. This includes doing nothing at all.
Forming a pact early on is essential. It not only gives you an excuse if you lose, but more importantly, gives your enemies someone else to attack other than you.
Avoid picking fights with the player whose turn comes right after yours.
If your attack is going well, you have walked into an ambush.
The enemy diversion you are ignoring is usually the main attack.
Try not to annoy the AI's, it tends to irritate the humans directly around you.
One rule to remember if you're hosting a game on a Classic Part Deux (or Semi Deux) board: 20% continent bonuses = marathons.
Always remember to shower compliments on other players, even for the most mundane victories. When these other players are deciding who to take out first, the good karma you have built up will help.
If you have worked for ages to build up a secured area, don't forget to tell the enemy lest they mistakenly attack it.
Atomised, Adrianated, Vonified, and Preacherification are all valid nouns in Lux. Well, except for Preacherification. That's a gerund.
When choosing a nickname, take something simple and easily remembered. If you have a long complicated name you will notice you tend to get attacked a lot more. This is because other players would rather knock you out than type your name in the chat whilst talking to you.
Don't ever be the first, don't ever be the last and don't ever volunteer to do anything.
If it's stupid but works, it isn't stupid.
Never forget, if it looks as though you are about to get beaten, and you are one turn short of getting the cards required to turn it all around, the old "hide in Japan" trick often works. There is a similar "hide in South Glamorgan" trick available on the UK map as well, but it works for any small country. The idea is to subtly place all your armies there, completely obscuring the background colour so that the aggressor simply storms past you thinking that you are one of his colonies. Sounds stupid I know, but you wouldn't believe how often it works.
Always be extremely suspicious of new custom maps, especially when playing them against their designers.
Don't stockpile armies, it makes you look conspicuous. Of course, this doesn't explain why you can often drop in on games of the highest-ranked players and see 2000 armies on one territory ...
If you're protecting a continent, always have a few visible armies on every country in that continent. When your enemy is skimming the board looking for an easy target, if he sees lots of icons on your continent, it doesn't matter how few there actually are in each country, he'll still subconsciously think that there are a lot of armies there, and be intimidated. This is another trick that shouldn't work but does.
When chatting, vague is good, lest you be held to something you have previously said. Comments such as "Shall we take out the AI's first?" and "Truce in Mexico?" should be avoided at all costs, to be replaced instead by "Shall we take out the AI's first where possible?" and "Truce in Mexico for now?"
If you're new to hosting, don't set up your room with default colors for all the players (especially not that putrid yellow color).
There are times, albeit rarely, when being nice actually works.