There are lots of topics you could choose from depending on the group of audience you are trying to reach, or what type of things you are most passionate about.
Just in case you are having a hard time trying to figure out what to say or do, here are some ideas to ponder on.
1. Start with your Talent - I'm pretty sure that everyone has God-given talents to share with the world. And talent is not limited to singing, dancing, jumping over a ring of fire, or painting. It can be any skills that you are really good at. You have worked hard to learn and develop this skill and therefore you are entitled to claim it as your talent.
2. Follow the Trend - it's not a sin to remake whatever is trending on the internet, and it will not hurt to give the original maker some credits too. Let's say you saw a very cool slime recipe on YouTube and you tried it yourself and made a DIY video. Make sure to tag, mention or thank your source. There are so many videos right now that are popular like what's in the box, food challenge, Q&A, shopping hauls, real food vs gummy food, try not to laugh, try not to be scared, try not to cringe, try not to be impressed, and more. You name it! The good thing about remaking these videos is that you get good chances of being clicked. Due to the entertaining satisfaction people get from these vlogs, viewers always come back to see more of it.
3. Do DIYs & Tutorials - YouTube has now become the "go to" place of people who are trying to learn new things or to improve their existing skills. I know someone who learned how to play guitar just by watching free lessons on YouTube. It's an indication that online video tutorials are effective and being followed by a lot of people to be good at something. Some other examples are doing makeups, photoshop editing, origami, sewing, stitching, video editing, photography, home improvements, gardening, math & science experiments, food preparations, arts & designs, gaming, and computer techniques.
4. Share Your Life & Passion - famous YouTube personalities started by just sharing what they do everyday. But before you do this, make sure you understand the dangers of giving too much information online and set your limits on what to let your viewers see. It can save you time doing the editing part as well. I have been seeing creators doing travel, adventure, job for a day, fitness, and pregnancy journey. There are so many things you can do to start launching your dream of becoming a YouTuber but doing the things that you are most passionate about is the best and more likely to keep you going every day.
That's all for now and I'm hoping to see you succeed on everything that you will do!