1. speak slowly. If they are looking at you blankly, chances are their brain is trying to catch up to what you just said, but you said too many words too fast and something is short circuiting. One word at a time, please, and put pauses between them. The first thing a language learner needs to figure out is how to hear where one word ends and another begins. (That's when they unlock the skill of asking "what does ___ mean?" or looking words up for themselves.)
2. repeat yourself. and slooooowly. If you said a bunch of words and they didn't understand, chances are they won't understand the next bunch of words you fling at them either, especially since they are probably still trying to catch up to the first thing you said and won't even register any of the new words. Give them a chance to re-hear the words you first used before you move on to new ones. They might already know what you are saying, but it often takes a couple tries before a language learner can recognize a familiar word in an unfamiliar context.
3. use simple sentences. Subject, Verb, Object. Stop it with all of the extra words you use to make yourself sound like a normal person. Sound like a baby and start small. Subject, Verb, Object. If you don't know what those are, look them up, and then give the language learner credit for probably knowing more about the structure of your own language than you do.
4. use gestures. Subject (point to the thing), Verb (mime the action), Object (point/draw/mime/whatever you need to do. Just repeating a word that the language learner doesn't know will never teach them what that word means. Help them along with a visual. It might jog their memory about vocabulary they've been studying or you may teach them something new!
5. be patient. People trying to learn a language are brave and also scared. Don't act out your frustration or stress with the situation--they were already frustrated and stressed when they were persuading themselves to talk to you in your language. Smile encouragingly at them. If communication still doesn't work, gesture apologetically and try to find someone to facilitate your interaction. Remember, an experience doesn't have to be perfectly successful to be a positive boost in this person's language learning process. You are helping them be more fearless in their trying, which is the most important part.
