Even if you don't have much of a budget for clothes, it's good to know what the trends are so you can always look in style by pairing your existing pieces well. Or if you are going to buy something new, it still helps to know what's in style. That way you can make the most of your hard-earned money.
How to keep on top of what to wear? Well, there's WhoWhatWear, a blog which covers not only celebrity fashion, but also fashion at cheaper price points for you and me. Still though, there's a lot of reading on WhoWhatWear, and it's not always practical to look through all of it. It can seem a little overwhelming at first glance. But they have great advice and it's a decent starting point.
Pinterest is another great option for fashion inspiration and getting outfit ideas. I find it runs a little slower than I'd like at times, which can be frustrating for the busy person. It can also be rather hit-or-miss and depends if you've picked sensibly as to who and what topics you're following. Used wisely though, Pinterest is a good way to keep on top of fashion trends. I do wish they'd let people browse without having to bother signing up, because that would be ideal. I prefer it to Instagram because you can click through to items on Pinterest.
I also like Wait, You Need This - a gorgeously stylish yet surprisingly down-to-earth fashion blog. Janelle from Atlanta runs this, and as beautiful as she is, she's also practical. You can see how you would look in these clothes because she picks pieces that are great not just for her but for others too. She steers away from freakish-looking and impractical items. Yet, the styles she goes for - WOW! And she makes it seem simple to look like her. (I'm sure it's not that easy though! - she's stunning!)
Those are just good places to start that I recommend. There are so many more fashion blogs that help with what to wear. Ultimately it's best to pick something that works for you, regardless of whether it's on my list above. Fashion inspiration can come in so many different ways.