Every time I have started a log I would find it to be a hard task because I didn't know when to log and I wasn't sure if I'd remember every milestone-like thing my tamagotchi achieved that day.
If I have to post about [almost] everything my tamagotchi does, I might get bored!
Another thing is is that I like to run only one tama at a time, for some reason I'm not sure of.
Can anyone give me tips on what makes a good log?
How to make your logging experience more fun?
What if I decide I want my tamagotchi to be an oldie? How on earth could I log about that?
Logging, I believe, should be for your benefit. You do it because it's fun, because you like keeping a diary about your Tamagotchis, or whatever reason you have.
There is not any fixed style to logging; some people prefer just writing it out, some people like making their Tamagotchis talk in posts (known as "conversation logs"), and some people primarily focus on pictures and narration. A good log can be many things, and it depends on the person, but one of the only things I think is a must in a good log is proper spelling, grammar, and punctuation. That makes anything (logs, stories, essays, fanfiction, etc) easier and more fun to read.
In order to make logging fun, you should just do what YOU want to do, not what anybody else wants. Don't do it just to get attention or get popular. If you like taking pictures and posting them? Go ahead. If writing conversations is your thing? You go do that (just don't copy people's ideas in a conversation log. That's a huge no-no).
I personally log because it's a way for me to unwind and write about things I want to write about. I don't like having to write about one specific thing; I like writing about a large variety of things in one piece (hence the weirdness of my log). I log because it's fun, and it's what keeps me running Tamagotchis so they get their money's worth of use.
If you want your Tamagotchi to be an oldie, you can go do that. It might be easier just to post pictures once in a while of your oldie doing some animation or using an item or something...that's usually sufficient for a post.
If you're still not sure, go look around TT, TZ, tumblr, or other places for logs to draw inspiration from. TT for sure has a pretty big variety of logs (some pictures, some written, some conversation), as does TZ. Read people's logs, comment about them, ask questions!
That's pretty much all I have to say about logging. it's a lot.