Structure is necessary, it keeps things organized but unplanned topics can also present great learning opportunities. If the student is excited about something, we talk about it! There are always chances to learn new vocabulary words and even hit up some practice with grammar. After all, conversation is just that, going with the flow and seeing where things go. Be spontaneous amidst the structure.
Another aspect that is helpful and fun is to center lessons around my students. It's their life and their experience they'll want to share, so we work around that.
Kids games are fun even for adults! It's okay to play "Ispy" (Yo veo) when we are learning colors or talking about specific vocabulary. We even play scrabble for those who really want a challenge. It's a wonderful opportunity to see how many words you already know and learn new ones when I play words you don't recognize. Jeopardy is also another great game I like to include. If someone wants to play chess or card games in Spanish, that's fine! There's always a learning opportunity.
I like to include real situations, finding little question cards or ice breaker topics is also fabulous for stirring the imagination in the target language.
Lastly, learn something completely new. I came across a wonderful webpage in Spanish that shares short articles on a variety of topics including pop culture, science, history, nature, the body and mind. I'm always learning something new and enjoy using the articles to teach my students new vocabulary and practice grammar.
Happy language learning!