[Dedas]

My advice would be to remain passive and trying to hide your strength - play (almost) defeated. Make the other players feel guilty when they smash the small groups of units you - in a (seemingly) hopeless attempt to save yourself - try to defend with. Let them see you as non threatful.
When you've managed the above you can finally start making peace with the strongest (because to them you are most insignificant) of your enemies. Try to offer them something non threatful (to them) in return for your loyalty. Examples would be information or letting them dictate how much area you can have to "live on". Let them think they have total control over your actions.
When that is settled they will focus their energies on the more threatful weaker allies. That will give you some breathing room, but don't make too big moves as the enemy you have come to terms with will start to suspect something.
Play two games, one for your "ally" and one in secrecy. Give him everything he asks for and at the same time build up your forces in a distant province (try to teleport somewhere) you know he will not look at or won't suspect.
At this time your "ally" will probably also be in war one or several other players - players you will help him attack - but at the same time you must make deals with them. Promise them to attack your "lord" from "within" when the time comes. In the meantime you and they attack each other just for show. Let your "lord" see that you are useful and loyal.
But always remember while doing these things: play and act naive, stupid and pathetic, don't show strengths such as resourcefulness, initiative and "cleverness".

When the wall of deceit is built and your "lord" is in war with several others due to you helping him expand his power, you and your allies strike - you strike hard and fast. But try to convince your allies that the operation will not work (you are too "weak") unless they take on his main forces (give them the coordinates you probably have due to being a loyal snake)". When their forces are being blunted you can grab the rich back country regions and finally start building up world domination again.

Remember, mercy can get you far but not against a merciless enemy. So don't try this with those or they will only laugh at you.

Good luck!