Characters advance in level by overcoming challenges ranging from combat situations to diplomatic encounters. All of these are symbolized by experience points (XP). Many GMs choose to simply keep a list of all the encounters PCs overcome during a session, add together the experience points, and award them in a lump sum at the end of the session. That way, if characters earn enough XP to gain levels, you won’t have to pause the game while they level up their characters, and you can instead let them do so between sessions.
Every opponent, trap, or obstacle the PCs overcome (including starship combat and vehicle chases) is worth a set amount of XP, as determined by CR. Purely roleplaying encounters are generally assumed to have a CR equal to the Average Party Level, but you may award XP as if it were higher or lower, depending on difficulty. Note, however, that encounters with a CR of less than the APL - 10 merit no XP award, as they’re too easy. Similarly, using starship weapons against a settlement or driving an asteroid into a planet may kill thousands, but in such instances, the party should generally not receive XP or wealth, as these massacres are neither heroic nor challenging. Experience gained in a fight comes not from enemy death but from expertise acquired as a result of combat, which such impersonal situations lack.
To award XP, take your list of defeated encounters and find the value of each encounter’s CR under the “Total XP” column on Table: Experience Point Awards. Add up the total XP values for each CR and then divide this total by the number of characters. The result is the amount of XP each character earns. For a slightly less exact method, you can add up the individual XP awards listed in the table for a group of the appropriate size. In this case, the division between characters is done for you.
In addition, don’t be afraid to give players extra XP when they conclude a major storyline or accomplish something important. These “story awards” can consist of any amount of XP. While a good rule of thumb is to award twice the XP for a CR equal to the group’s APL, you can also customize your story award amounts to help your players’ characters reach a particular level for the next adventure you want to run.