Any advice for the novice speaker?

That's a surprisingly difficult question. I've improved slowly and unsystematically, and to the extent I’ve succeeded, I think it's because I was trying really hard. So maybe the most useful tips I can give you are about how to try really hard: First, identify yourself as a nice person, someone who always tries to be kind, so that if you hurt someone, you’ll think, “That’s not the kind of person I try to be.” Second, attempt things that require you to be nice in order to be successful—teaching and health care worked for me.

Here are a few (not particularly original) suggestions on practical niceness:

• Smile a lot. Pay attention to what your body language is like when you interact with animals and small children (assuming you like them), and try to act more like that toward everyone else.
• Be interested in people. Make mental notes of the interests and characteristics of the people you talk to, especially things you like about them. Ask questions about things that seem to interest them.
• When someone seems upset, indicate that you have noticed this and are concerned by it. Exactly how will depend on the situation (it may be best not to draw attention to the problem), but it’s basically never the right answer to ignore how someone is feeling or act as if it’s unimportant to you.
• Disagreeing is very tricky. Most of the time, arguments are veiled hostilities at least as much as they are exchanges of ideas, and if you start an argument you will almost inevitably find yourself in a status war. Before you open your mouth to disagree with someone, consider whether you are starting an argument, and be very, very careful.
• Keep in touch. Quick notes, texts, phone calls, etc, don’t take much effort, but they’re important to people.
• Be appreciative. Thank people a little bit more, and in more detail, than you’re used to. If you’re like me, you probably often notice good things about people that you don’t mention—this is a missed opportunity to give a sincere compliment.
• Patience is often necessary. Sometimes someone wants to yammer on about something that bores you, or demands your sympathy when you think they’re being wrongheaded, or just needs some time to get over their mood. You can become more patient with deliberate practice.

(Note that I suggest these as ways of being nice to people, not of making people like you or of accomplishing any other goal.)

Have you heard of the trick where you can get people to like you by getting them to do small favors for you? Examples include getting them to: loan you a book, help you through an important decision, or watch your dog for a day.

You can reverse this trick, and make yourself like other people by doing small favors for them. Offer to loan someone a book, offer to pick up a tab for something small, etc.

Before you know it, you'll like everybody. Actually liking everybody leads to being nice.