I'm tempted to do a thread on the subject, but I'm very aware that I don't want to take credit away from the excellent thread by SFraser over in the Tactics section of SI. I'll think about doing something though, as I know that the thread isn't likely to be readily understood by a wider audience who just want to know what option to choose and when.
With your specific examples, I want to make a proviso before answering - different players respond differently. And their response will also change depending on circumstances. So the skill is spotting when the circumstances are the same and then use that knowledge for that specific player. It means 'knowing' your players. A good general guide to start learning is that players personalities seems to be linked to how they respond because the responses seem to be based on hidden mental attributes. However, even with personality types there is a wide range of different possibilities...
Complacency - I use 'go out and prove a point' (if available), or the 'not pleased' option. Occasionally 'angry' if the performance is very bad, however if it's that bad, then I'd be more likely to substitute the player. Note that complacency might not be a bad thing - a complacent player is also relaxed and some players play better when complacent (Sam Gargan (starts at Brighton) is such a player, SFraser on the SI boards says Berbatov is another).
Nervous - 'no pressure' or 'have faith'. Low morale would incline me to try 'have faith' as that seems to have an impact on morale. If the player is nervous but playing well, encouragement or pleased might be better options.
Poorly - 'go out and prove a point' (if available) or displeasure. Similar style to how I treat complacency really but with no doubt that poorly is a bad thing. Another thing to check out is why the player is playing poorly - if it's low morale, then 'have faith' or encouragement may be better options. If performance is still good, pleased might help out too.
As I said, these are general guidelines from which I start. There can't be specific rules unless one wishes to do it for every player in the game for every circumstance likely to appear. One thing I have noticed is that 'extra options' (eg 'prove a point', 'expect better') always seem to be provided for a reason. It is not worth using them all the time (counter-productive in the long run) but do help for short-term impact when used sensibly.