To get the best possible vocal performance (and to avoid breaking your voice during the first song), singers should warm up, just like sportsmen do. Many different schools offer different techniques to achieve this, but considering it's your body we are talking about here, you should try to find out what works best for you! Nevertheless, here are some pointers for you to start gently and calmly!
And if you're too lazy or busy to properly warm up, at least make a decision not to sing too high or too loud when you first start singing during the day or evening. Don't forget, you can warm up while you're driving or riding somewhere.