Comrade has two opposite victory conditions: the party victory, requiring the possession of the informer card, and the freedom victory, requiring the possession of any card but the informer card. Nevertheless, playing for one victory condition doesn't exclude the other so both should be part of your strategy.
Party victory can be achieved either passively, by someone playing you the dissident card, or actively, by you playing the informer card to the dissident. The passive victory is beyond your control, although a good poker face helps. The active victory is more controllable. Whenever you see the dissident card, keep track of where it's going afterwards as it will help you localize it if you get the informer card.
If you played the dissident card to a player with 0 cards the previous turn, it will still be with the same player. If you played the dissident card to a player with 2 cards the previous turn, it will either be with the same player or with the player that got 1 of the 2 cards. Thus, your search for the dissident will be limited to up to 2 players after one turn and up to 4 players after two turns. Make sure that you remember those players. After 3 turns it may be more difficult to trace the card but since players generally try to play the dissident card to new players, a good guess is that the card hasn't returned to the players who may already have seen it.
Needless to say, you should never play the informer card to a player with 0 cards, since this will give away the informer card without any chance of finding the dissident card. If you can't do it in the early game (before enough players have seen the dissident card), you should keep it and try again next turn. In the later game, you should give away the card anyway to avoid the risk of losing in a freedom victory.
Freedom victory is achieved if the chairman succeeds in calling the players who have seen the dissident card. To improve your chances of freedom victory, you should keep track of the dissident cards just like you do when you play for a party victory. In addition, you should keep track of the informer card to avoid calling him or her to the vote.
How to Vote
A freedom victory requires a vote for freedom. Should you always vote for freedom then (that is,
as long as you're not the informer)? Not at all. A vote for freedom also reveals secrets in the game.
The informer may use the freedom votes to trace the dissident. The informer may even be among the
voters and vote for freedom to have the dissident revealed. So how do you know when to vote and when not to vote?
One simple rule is not to vote for freedom in the first turn and usually not in the second turn either.
The main reason is that the dissident card won't have been seen by enough comrades to vote for a freedom
victory that early in the game. Furthermore, the dissident will know who else has seen the dissident card
(namely the player who played him or her the card and the player who played that player the card) so
there is no need to use the freedom vote as a signal for the dissident to play the card to someone else.
How about the later turns then? Here, it may be more important to help the dissident know which
comrades that have seen the card (namely the ones that vote for freedom) and which haven't seen the card
(namely the ones that vote for the party).
How about the informer then? Well, given the discussion above, the informer should vote for the party
in the early turns (since a freedom vote may be interpreted as a false comrade vote and reveal the
informer) and possibly for freedom in the later turns (to find out where the dissident is and play the
card to him or her).
Why only "possibly" in the later turns. Because the informer reveals himself or herself as well.
If the informer is the first player that gets to interrogate after the vote, he or she will be able to
give the dissident the informer card before any other player can interfere. However, if the dissident is
before the informer, he or she will be able to give the dissident card to another player, who will then
have two cards and not be allowed to be given the informer card. Likewise, if any other player is before
the informer, he or she will be able to give a card to the dissident to prevent the informer from
doing so. Remember that secrecy is the informer's best weapon for victory!