If someone is struggling to understand you, try the tips below:-
Speak more slowly (not louder!)
Keep it simple. Use words that are most common. For example, if you want to say cat, don't use the word feline.
Keep it short. Use basic sentence structures (subject/verb/object).
Don't worry about pronouns, instead use the names of the person or thing you are talking about.
Use a lot of hand gestures. "Do you mean up?" Raise up your hands to help the person understand the word.
Use sound effects. You may feel silly, but if you are trying to tell someone that something exploded, using the sound "Ka Boom!" will get your point across!
If you have a smartphone, find images to illustrate what you want to say. If you have pen and paper to hand - draw. (You can practise your drawing on the drawing app Pinturillo).