As a DM team, we want to understand what drives our players and their PCs so we can tailor our events to their enjoyment. We can also help players to flesh out their characters, to understand the setting, to enhance RP and to reduce inconsistencies.
The two main tools we use here are Tells and observation. Because there's no sense in asking a player the same thing over and over, use the forums to share your theories with the team.
There are three interventions you can perform in this role. The first is awarding XP, the second is adjusting alignment and the third is coaching a player. They all depend on an understanding of player and character motivation.
As DM you have the ability to award PCs experience points even outside events. There are two reasons to do so. First, to reward the player for extraordinary energy put into the game. This is most obvious when they go to lengths to get other players involved in their activities, but can also be a more subtle show of effort. If the effort isn't linked to a specific character, ask them which PC they think should receive the bonus. Second, to reward a player for playing a character consistently and in line with the mechanics. A good time to do this is when they make IC choices which may be to their detriment but satisfy their personality. Always explain why XP was awarded. As for the height of the award, consider that most characters advance at an average rate of 75-100 XP per play day. And to prevent multiple DMs rewarding the same thing, remember to post the reason and amount on the forums.
Alignment adjustments should never happen without asking why a PC made a certain dramatic choice. You must be aware of a PC's motivation before you can decide to which of the nine alignments it belongs. In almost all situations, alignment shifts by 1-2 points (a CN PC performing a LG act gets +1 good point and +2 law points) and only one adjustment should happen in any given week, with exceptions for radical behaviour. If a PC's alignment does not change for a few weeks, consider moving it deeper into the field it's already in when a good opportunity presents itself (or is presented by you). We change alignment points to show the consequences of a choice. For players, this is validation that their PCs are noticed and a visible reflection of the character's struggles.
Coaching is used to help others improve their play. As DM, you should take an active role in making sure players who struggle can learn to earn RP XP. Ask if you can give them some pointers. Tell them you noticed something unexpected and explain why you think it's wrong. Ask them if they agree and discuss how you can improve it together. Be as constructive as you can, in the understanding that each DM looks for different things and everyone picked up some bad habits in their life.
Player motivation can be categorized and scored in different ways. There is a Page with examples.
Character motivation tends to be more concrete. What they will and won't do is related to their background, group dynamics, shortages, fears, ambitions, dreams and general personality. Sometimes it's not so much about what is asked of them as the way it is phrased. Some PCs want to be persuaded, others are turned off by insistence.
You can find a lot of clues in a PC's alignment, deity, inventory, examine description and forum biographies. Listening to conversations and noting how they solve obstacles during events will also provide free information. Using Tells, you can get more specific and detailed information. As with ambient DMing you'll want to avoid disrupting immersion as much as possible. If you're not sure why a PC made a certain choice, it's better to ask for clarification as it happens rather than afterwards. Otherwise it's best to look for quiet moments. To get your information, you can ask direct questions or just strike up a conversation. Most players are happy to talk about their characters and you can learn what you want to know by listening and asking the right questions. Other players prefer to keep their character's dearest secrets close for fear of anyone including DMs using it against them. This is a rational fear, but see if you can liberate something anyway. When you talk with players, accentuate the positive things they do. Get excited about their characters and encourage them to dream of their futures. If something seems out of character, ask if it is. Either you help the player to fix an oversight or you discover something new. If you can learn what draws a PC into an event and what makes an event enjoyable to the players, we can all make our events more awesome.