There is nothing about fully ready for tournaments. S/he will learn along the way. S/he may make mistakes, such as forgets the touch-move rule, talks too much, etc. Let him/her make mistakes there, be corrected there. S/he may lose games, and s/he may cry. Let him/her do it. We grow up in this way. You don't need him/her to be a perfect model student before being allowed to play in tournaments. This is not performance on stage. This is real life!
No need to worry about tactics or strategies, let alone openings or endgames. They will learn these things later. Go there, compete, get excited, and get experience.