Prior actions to singing lessons

I started out on the guitar because I wanted to make music again. After a while the uke-fever kicked in and I now enjoy both. Unfortunately, this isn't enough for me and I would like to add some vocal support to my playing. Because I am quite sure that I need lessons (my range is very limited and my voice is shaky). I would like to know what I can learn/train before I take some lessons.

As an example:
- before I started my guitar lessons, I've spent some time understanding chords and I was able to write them down as tabs and I was able to play them on the guitar.
- before I started my driving lessons. I've spent some time learning the theory behind traffic rules.

Just to be sure. I do not want to risk damaging my still weak and limited voice. But I do not want to spend a lot of money on thinks that I could have done at home.

An additional question to this. Is it better to start with private lessons or is possible to get the basics from group lessons. I am asking this because the latter might save a lot of money.

Learn how to breathe. Learn never ever to strain.

I don't have the time or money for lessons, but I have been having really good success with Jaime Vendera's "Raise Your Voice" book. It's written for rock singers, and therefore horribly, but I have gone from a range of F on top of the staff to being able to sing high B's full voice, with the ordinary range being much easier.

I've never had private lessons but I did have a 4 day intro group lesson. And I think it was very helpful to learn the basics and build a foundation of good singing. There are so many little techniques, and nuances to getting a good tone that I think it's worth it to take lessons first, and possibly learn things on your own later. for me I started off playing saxophone when I was younger and dabbled with piano and didn't take singing very seriously until a few years ago, and I've noticed that some people are naturally good singers, and others have to work it at, but anyone would benefit from good singing lessons, the trick is to find a good instructor.

I think before starting lessons, you should research breathing techniques and practice applying them to your singing. My friend took 4 singing lessons ($30 for 30 minutes) before she couldn't pay for them anymore and she told me the majority of the time was focused on how to breathe and I feel like that's really a waste of money. If you practice your breathing beforehand a teacher could tell you what to fix and you could probably spend that time on something more useful.