Go for numbers early.
When the map is still mostly empty, it seems like quantity of troops is slightly more valuable than quality.
I'm willing to give up a coin or two on the first round to get a few more troops.
Decline early to get two races working for you.
Don't be afraid to abandon all regions and relocate all your troops. Sometimes this is a very good thing to do.
Try to place troops on mountains before declining. They'll hold out a little longer there.
Don't just look at your race/ability combo in isolation.
Look at it also in terms of how much it can do to hamper the efforts of the player currently winning the game (or the player most likely to stop you from winning).
Target 8-11 points per turn once things get going.
Overextending yourself is dangerous.
Dwarves deserve special mention: they are terrible.
You should have at least 2-3 races over the course of the game.
The Active race has a lot of work to do.
It needs to take lots of territory, take defensible territory (to keep getting points while in decline) and also mess with the opponents: oust them from defensible areas and force them to go into Decline at points that are disadvantageous to them.
When your previously declined race has been wiped out or has been reduced to 1-2 territories that look like they won't last long, then go with your active race into decline.
I believe that you need to earn VPs from declined empires as often as you can.
It is better to decline too early, than too late.