Time management questions

I have some doubts around time management –
1. Distractions: Some of my main distractions are over worrying about what will happen in the future, over planning about future, regret about some things in the past, over analyzing decisions I need to make. How do I move forward to eliminate them?
2. Procrastination – sometimes it can be good, for example I took a long time to hire a nanny and because I spent the time to look for the best I got the best .. so in this situation waiting to take a decision from candidates I had turned out to be the best.
3. Multitasking – I sometimes multitask when I am finishing an activity at work and check my phone in parallel. It can sometimes act like a mini-break and then I can focus better. Is there anything like good multi-tasking?
4. I struggled to find what can I say no to, can you help me here?