I don't tend to have problems with words (spoken or written) when I do mean it but I like to put them in a larger context. For example, express my appreciation for something the T helped with, a particularly interesting session or idea, or share how something from therapy affected my everyday life. If there are things I particularly relate to regarding the T's behavior and what he shares - or the opposite, if something feels very alien. I like to express both positive and negative feelings in this more complex, descriptive way (rather than just "pure" feelings) not only in therapy but also in general. Also with associations and comparisons.