You have the power of theft

(From the official description at Cosmic Encounter Online) - After you and your opponent have revealed Encounter pods, you may steal your opponent's Encounter pod before it is jettisoned. The pod will be moved into your console for your future use. You may steal a pod only when you are a main alien in an encounter after your opponent's pod has been revealed and would normally be lost.

What does this mean?  It means that there are times you hope opponents play their best pods against you, since you get to steal them.  Other players may be reluctant to use their best pods on you, as they may be seeing them again soon when you play them.

Example:  You are the defensive player in an encounter.  You play a 10 and the offensive player plays the 40.  You lose, but you can steal the opponent's 40 and use it on a later encounter.

After Filch has made the decision to steal, Filch can be zapped.  In such a case, both pods used in the encounter are lost (as they typically are after an encounter).

Filch has the choice as to when it steals pods.  Simply put, there are many occasions where pods should NOT be stolen.  For example, if you have a hand full of 10s and 12s, and your opponent plays an 8, you should generally NOT take the 8.

While it may seem obvious that you'll want to take the biggest pods that are played against you, the pods that you take should depend on other players in the game.  If Anti-matter is in the game, you'll want to collect small pods as well.  If you're in a game with Pacifist, you may want to collect negotiate ("N") pods.

If you acquire a big pod such as the 40, other players may play an "N" against you to try and collect it in compensation.  Thus, you may want to have some smaller pods as well to discourage this.

If all you're running out of encounter pods and all you have is smaller pods, you may want to avoid collecting any additional pods so that you can eventually get a new hand.

SPECIAL NOTE REGARDING CLONE:  Filch is the mirror image of Clone.  Clone keeps its pods; Filch steals the opponent's pods.  In a game with Clone, you'll need a quick trigger finger for your mouse.  When you and Clone are in an encounter, both of you will be able to grab Clone's pod at the end of the encounter.  Whoever clicks first after the encounter is over gets the pod.  Timing is everything.. 

Be wary of playing your largest pods against Filch, especially when Filch has three bases.

Keep track of what is in Filch's console (i.e. which pods Filch has).  Play a negotiate pod to get consolation from Filch when you think you can acquire one or more large pods and when it won't otherwise adversely affect you.

Use zaps against Filch sparingly.  Filch isn't particularly powerful unless Filch acquires one or more large pods with two or three bases.

IF YOU ARE CLONE:  the note above in "Playing as this alien" applies here.  Timing is everything.