How to wake up the voice in the morning?
Warming up plays a crucial role for any professional and not professional singer or anybody who is going to sing. It is important to establish several things that work best for you. Waking up in the morning is difficult process not only for your voice, but for the whole body. That's why is important to wake up the body first. You can take a warm to hot shower, which will relax the muscles and will increase the blood circulation. The next step should be some stretching exercises. The neck and the shoulders are usually problematic zones especially if you haven't had good sleep or some of the muscles are sore or ache, or you just feel stressed. Some simple stretching movements could help relaxing those parts of the body. For instance: circle movements with the neck, stretching it to the left and right, front and back, rolling the shoulders and the arms. You can even run on place or jump. Nothing heavy of course. Light yoga is also a good solution: "sun salutation" or a couple of "warriors poses".
After waking up the body and the muscles we can proceed with the voice.
Everyone takes time to warm up their voice, so you should let it take its time to warm up too.
1. Lip Trills or/and Tongue Trills
A good exercise to start with is the so called "lip trills" or "tongue trills". I usually recommend 2 exercises of "lip trills", the first should go to the transition or the break of the voice and the second exercise should cover it. Then the "tongue trills" will loosen easily any tension at the back of the tongue. The tongue trill exercise can cover 2 octaves or less. If you feel tension then the muscles are not ready yet, so always be gentle and do not push or force anything.
Examples: "Do Re Mi Fa Sol Fa Mi Re Do" or "Do Mi Sol Mi Do" or "Do Mi Sol Do Ti Sol Fa Re Do" or "Do Mi Sol Do Sol Mi Do"
2. Humming sounds
The humming exercises are the best to continue with in my opinion. You are not vocalising yet, giving the vocal folds more time to get ready and in the same time you are finding the best resonating sound for the voice. It seems quite simple, just say "Hmmmm", but it can be misplaced. As we go higher in pitch the buzzing sensation should change. First it should be felt a little bit in the chest (for low pitch voices), in the lips and mouth, after that in the nose or nasal area and in the high register will progress towards our eye area and upwards towards the head.
Examples: "Do Re Mi Fa Sol Fa Mi Re Do" or "Do Mi Sol Mi Do" or a combination form both of them, or "Sol Fa Mi Re Do" etc.
Practising the humming warmup exercises together with the other vocal warmup exercises will ensure that the voice is properly warmed up and this will also avoid any unnecessary damage.
3. Sirens
Yes, they can be painful for your neighbours, but they are an absolute must in the warming up session, again in my opinion. They provide smooth transition between the trills, the humming exercises and the actual vocal work.
The examples I can give are not very different from those above. Simple sliding scales from "Do to Do", descending and ascending movements or on a perfect 5th - from "Do to Sol"
4. Vocalising
Now is the time to hit some notes. Choose first the most comfortable vowel for you and then move to exercises that use different vowels. And do not forget that the only thing that actually changes the vowels is the tongue.
All the tips and exercises above work best for me. Yes, some of them I use in my daily practice with my students only if they suit the student and he/she feels comfortable with them.