Back when I just got out of the military in 89, I joined a band where I was forced to learn backups/harmonies/sing lead on 2-4 tunes. Up to that point I hadn’t done much vocally in my other band I had in HS. Our bass player was the lead vocalist and gave singing lessons out of a mom/pop music store. Since I had a decent ear developed from picking songs before tab really existed, I started concentrating on picking out each part in a 3-4 part harmony tune like Kansas or Queen, Journey etc. The biggest help/tip I can give is this: sing to your favorite songs in your car or at home. Put some power behind it; don’t hold back. Repetition is key just like guitar. Do it every day. You’ll hear yourself if you aren’t hitting the note right. I did this every day on the way to and from work, school…after a few months my voice and range got stronger/better. The more you do it the better you’ll get.
After that band, and going forward 6-7 years I’d become the lead singer in our 3 piece. 40 songs a night. AC/DC, Journey, AIC, Queensryche etc I could sing it all. Not on the level of those great vocalists but I could at least hit the notes.