Someone asked a question
Hi ^^ this is probably a stupid question but I don't know if I should speak/write using plain form (ある、だ) or polite form (ます、です)? Maybe I'm overanalysing this ^^;; I want to sound natural but I don't want to come across rude either >

Hi, thanks for reading my Tumblr~. I don't know in which situation and to what kind of people are you going to speak, so I can't say which to speak with.

If you're making a presentation in a meeting, you should use formal ます、です. 

If you're selling something, you should use the polite form.

If you're talking to your friend, use the bare form.

For example, if you want to be polite,

私は１４歳のダンサーです。アイドル志望で、毎日歌と踊りと日本語の練習を一生懸命がんばっています。皆さん応援してくださいね！

If you want to be more friendly,

私は１４歳のダンサーだよ！アイドル志望で、毎日歌と踊りと日本語の練習を一生懸命がんばっているの。皆さん応援してね！

If you drop the certain particles like the following, it gets awkward.

私は１４歳のダンサーだ！アイドル志望で、毎日歌と踊りと日本語の練習を一生懸命がんばっている。皆さん応援して！

It's as if Jack Bouer is speaking. Of course it comes off as rude in most situations.

Jack Bouer voice-over is like this:

俺はCPU捜査官、ジャック・バウアーだ。CPUの本部はロサンゼルスにある！クロエ、衛星につないでくれ！