MS Word Alignment Problems

I've had this problem for a while and I'm not sure exactly how to fix it, but I almost always get it to work. That said, since I don't know why or how I manage to fix it, maybe you do:

I have a piece of text. I center it. I type things down. I press two return keys, and I want to type in left justification. Easy as pie? No, the entire piece of work (or most of it) becomes left justified. This is irritating and I don't know/why how to fix it/it happens.

Type everything first as if you're typing in notepad, format afterwards. This is why WYSIWYG processors are evil, it tempts you to format as you go which wastes rather a lot more time than you'd like to think because things keep jumping about that you don't want and you need/want to keep adjusting things here and there :p