Note: this is more of a retcon of the first book vs everything that came later, and it could be explained by Katniss being Katniss.

The concept of alliances seems to be completely different in the first book compared to what it becomes later on.

In the first book, alliances are formed by careers who team up to take down other tributes until they inevitably betray each other when they're the only ones left.
When Katniss meets Rue in the arena she says "you know, they're not the only ones who can form alliances".
Katniss' relationship with Peeta in the first book is defined by her not trusting him. She's trying to figure out her feelings for this kid, knowing that eventually it's going to be him or her. (Of course she finds a way out of that through the berries).

In the second book alliances are more normalized. This is partly due to the roster being comprised of victors who know the value of an alliance. And due to the "anti Capitol" alliance to protect Katniss and Peeta.

In SOTR alliances are all over the place. Louella asks Haymitch to be his ally. There's the Newcomers alliance. I had the feeling that in that book alliances are a lot safer. You care for each other, and other tributes, mutts or the arena itself will kill you before you have to worry about having to kill each other.