I agree with the points mentioned.
Objectivity. With a good announcer, in any sport, it should be very difficult to ascertain their personal feelings about the competitors. This is also connected to consistency. What's good or bad for one player/team, should be considered good/bad for all.
Background. The announcer should know the players well. Not personally, but at least in tennis terms. Even with a 128-draw slam, the announcer should know everyone in the field. S/he should follow the sport year-round, and thus be familiar with everyone in the top 100-plus, and thus only need to study up on a couple of players at most. No chortling goofily to yourself about how you've "never heard of" someone in the top 50-60. (I'm talking to you, Carillo.) If the announcers don't respect the sport, how do we expect the general public to?
A positive attitude. There are a lot of good things in the sport, and in each match. Bring them out. You don't have to be Pollyanna and pretend everything is great, but likewise you don't have to harp on only negatives. Promote the sport. Convince the viewers why we should be watching the match, not why we shouldn't. No droning on in a tone that makes it obvious you would rather be doing another match. You can still discuss issues and problems facing the sport, but let viewers know it's a good sport that is worth watching. You don't have to turn into Dick Vitale (please God, don't), but show some enthusiasm. For all the complaints about Barry MacKay, whenever you watched a match he did, you got the feeling that he's happy to be there, and happy to share the experience with us.
Don't say something unless you've got something to say. The time between points and games is an opportunity to say something, not an obligation. Make sure what you say adds to the telecast.
Analyze the match. Don't just report what happened, tell us why. When a stat panel says a player's first serve % is in the 40's, and they have 12 double faults, we can guess that they're not serving well. Tell us why.
Be judicious with annecdotes. They are like the seasonings on a meal. When sprinkled carefully, they can add just the right enhancement. When overdone, they can ruin the experience. (Who wants to eat a plateful of salt?) And if you spend too much time on silliness, it sends the message that the match isn't worth watching. If you want to work on your comedy routine, hit the nightclubs.
Each match should be a free tennis lesson. Analyze the players' strokes and strategies, and show us what they're doing right and wrong. In this instance, even a bad match can be useful, as it can serve as a teaching tool to analyze common mistakes. For example, someone watching at home might be about to give up the game because they're repeatedly driving their forehand into the net. If you show them what happens when a pro covers the ball, they might recognize their own mistakes and correct them, instead of quitting.
Bottom line is, respect the sport. By respecting the sport, they respect us, the fans. If someone is unwilling to show the dedication to follow the sport year-round, and promote it by bringing out its many positives, and present it in an impartial, professional manner, then they should step aside for someone who will.