Hi Siddharth:
Me again!
I found a good article on the subject that expanded upon my previous answer to your question:
https://www.quickanddirtytips.com/education/grammar/using-present-tense-in-a-story-about-the-past.
As I said, depending on the kind of message you wish to communicate determines which tense to use, especially in your second example.
However, in your first example, even though you're seemingly describing something in the past (the best place you have ever seen), you're actually describing your feelings in the present. As in: as of now, this is the best place you have ever seen. If you used "was", as in--the best place I've ever seen was--, then the reader could think this place is no longer the best place you've seen or the place no longer exists.
In your second example, the first two "was" only relate to something that happened. They are in the past and are no longer currently relevant. The fact that he is a doctor is something that is still true: it didn't just happen in the past: it's still true! In other words, you're no longer talking about him in the past; you're talking about him now.
I understand a possible confusion, however: what if your friend is say still wearing a white shirt? Well, a trick to know is that wearing a white shirt is not really an ongoing action (like probably being with friends). Those are temporary things that usually end. Having a job often is permanent (esp if he's currently a doctor).
That being said, as the article says and as life is, storytelling is often completely in the past tense, and switches to the present tense can be confusing. One way of avoiding the confusion is avoiding the problem entirely. For example, using your second case: I met my friend, a doctor, yesterday...
TLDR: there is not always a "correct" way. But if you remember the implications of each tense and one tense best first what you're trying to say, then use that! If it makes you uncomfortable to switch between tenses, try rephrasing.
Hope this all helps!!!
