Here is an example of a very simple warm-up, which also revises vocabulary items worked with in a previous class.
In this case, the vocabulary was from a TOEIC preparation class.
Toeic Wordlist Startup Questions
Students individually or in pairs complete the sentences. You need to explain they may need to adjust the tense any verbs are in to fit the context.
They then stand and circulate and ask and answer questions of each other.
Finally you can have them report on the most interesting answer.
(5 per sheet to save paper!)