As I've been working with my German students I've noticed a number of topics which many of them seem to struggle with and which none of the textbooks or practice grammars that I have really seem to cover adequately. Generally these tend to be semantic-pragmatic challenges; syntax and morphology can be drilled quite effectively, but producing meaning is much less mechanical.
1) How to talk about likes and dislikes
There are multiple ways to express this in German, but they don't really map neatly onto the English "I like", namely:
- x gefällt mir
- gern haben (with things) / gern + verb (with activities)
I don't use these three expressions interchangeably, but couldn't always say precisely why. (And of course, not being a native speaker, I can't necessarily claim that my intuition is representative of how most speakers of German use the language.
I've found that my students -- even ones who have already had a fair amount of exposure to the language -- often seem to feel vaguely unsatisfied with options 1 and 2 and want to use mögen instead. I don't know whether this is because they're still translating on some level when they speak German and want something that matches better with the English.
However, the problem is -- mögen is much more limited in its usage than either of the other options, and it can't typically be used as a substitute. Even though it's technically a modal verb, I rarely use it this way when it has the meaning "like". Far more frequent are the subjunctive (möchten, "would like", which has started to gain the status of an independent verb i.e., see here) and the epistemic usages of the verb (es mag sein, er mag das getan haben).
So -- what should one use when? gefallen expresses a judgement about something, whereas gern is more of a preference. Thus gefallen also tends to be more specific, referring to a particular thing, person, or place, rather than a broad generalization about an entire class of thing. (One reference suggests that gefallen can't be applied to food, which may be related to this.) On the other hand, gern can be either general or specific (both ich schaue gern Filme and ich habe diesen Film gern are possible), and it can be combined with a variety of verbs to describe activities.
mögen is used above all in negative and interrogative sentences; rarely in positive statements and often without a complementary verb. It's often used when talking about food/drink:
Ich mag moderne Musik.
Ich habe diesen Mann nie gemocht.
Magst du lieber Bier oder Wein?
Jetzt mag ich keine Musik hören.
2) Particles (doch, noch, eben, gar)
I learned these pretty much intuitively and I've been finding it difficult to explain them to students when they ask what they mean and how to use them. The problem here again may be that they're looking for a one-to-one translation and there simply isn't one. Often the best I've been able to do is say that they indicate a contrast or emphasis, but there has to be a way to show them how these particles work so that they not only make sense, but my students are able to use them themselves.
The most straightforward way to approach this is probably to simply list a number of basic uses for each of them, followed by examples. This is what most grammars I've seen do -- e.g. the entry for eben lists the following: resignation (Man hätte ihm eben das Geld nicht geben sollen); agreement (Eben das wollte ich auch sagen); negative stress (Es ist nicht eben klug).
But I'm not really sure that this is the most useful method for students who don't already have a good sense of how the particles are used anyway. These words are also highly dependent on context because one of their primary functions is as discourse markers -- to situate a response in relation to what has been already said, to introduce a topic, and so forth. So teaching the particles within the context of dialogues might make more sense.