6 some rules for when you can and can´t separate a multi-word verb
. You can't separate: verb + adverb (intransitive): He fell over. The plane took off.
. You can separate: verb + adverb (transitive): Cross out the word. Cross the word out. Cross it out.
. You can't separate: verb + preposition: I'm looking for my bag.
. You can't separate: verb + adverb + preposition. I get on with my neighbors.
These rules are useful for your reference, but would probably confuse students. The best advice you can give them is learn any phrasal verb with examples, which make it clear whether or not they can be separated.