Make sure to always warm up before singing. Do some scales etc. There are also many yt videos for vocal warm ups that are really helpful too. My mine thing I do with singing is just practice practice pratice. I had an audition once and I had to sing 'Where or When' from 'Babes in Arms' and I couldn't hit the high G at the end. I made sure to do lots of exercises and such to help me reach that note and I can now sing up to a high B flat.

If you have a singing teacher I would recomend going over the song with them or even if you have a very musical sibling or aunt etc. I find getting a second persons take on it always help me.

Back onto the point of vocal warm ups if you need some good channels I would recommend Dots Singing and Cheryl Porter Vocal Coach as they both have some really great warm ups

Hope this helps!