Definitely talk.
The biggest mistake I see people make is to say nothing to people.
I know I almost always ally with the first person to respond to me, because that means two things:
1. They're more open and friendly
2. They're more active as a player
Both of these things make a good ally.
For you, talking to everyone, even people you don't border, is always a good idea. You'll get more info from them, even if they don't explicitly give you any. Ask people things like, "Oh, have you heard from Red yet?" or "Any news on your side of the map?"
People like to feel heard, and the more people like you, the less likely you are to be attacked.
Tactically speaking, check your opponents' profiles to get an idea of who is experienced and who is not. Then, watch what the experienced players do with their specialists and who they attack. You can even ask them for advice upfront, if you want. People are generally welcoming in this game. But a big part of this game's strategy is knowing which specialists go together for big combos.
I personally think that finding one ally and sticking with them is more effective than stabbing that ally in the back. That being said, though, a big part of this game is knowing how to stab players. See, you don't want to look like a jerk, and you don't want to leave your target in a position that they can hit you later in the game. I won't tell you how to do that, though. I have to keep some secrets

If you're the target of a stab, then it's vitally important that you *don't* get mad. In fact, chat happily with your stabber. Be witty, have fun! Firstly, this makes your experience with the game way more enjoyable, and secondly, it makes your opponent like you more. I can tell you firsthand that people will turn on a dime and become your ally if they think you can help them, but they won't do that if they think you have a vendetta against them.
Most importantly, keep experimenting. I've been playing this game for months, but I don't ever play two games the same way. There is no best strategy in this game. Just find one that you enjoy, and then tinker with it endlessly.
Good luck!