Warm ups aren't just singing "la la la" until you feel ready to sing. Warm ups should be unique to your needs and set you up for the kind of singing you're going to do.
Start in your low range and begin in your chest voice right around the pitches where you speak (sometimes a note or two lower if you're feeling particularly high that day). Stay within an octave for a while and work on breath (lip trolls, etc.), articulators (tongue and jaw and onset (the initial attack when your vocal cords come together to make sound). Don't be a hero. Be gentle at first, especially if you are an aggressive singer.
Once you're feeling warmed upb then move on to exercises that address more of your range. More importantly choose exercises that line you up for the kind of singing you do: classical, music theater, R&B, Rock or whatever.
Get a good teacher to help you figure out what these are and you'll be in good shape!