1. First of all, when dressing for an interview, always dress professional and cover up. A few hours of being hot and uncomfortable are worth it because it may help you get the job. Suits for men or women are usually the best bet. Even if you discover the office is causal dress, you still want to be overly dressed in professional attire to show that you're serious.
2. If you have a job, check their dress code and ask questions if it seems unclear. It is better to check, ask co-workers or ask your boss if shorts or other hot weather clothing items are acceptable and appropriate before getting in trouble for wearing them.
3. Once you understand your company's dress code, now is an excuse to do a little shopping. Shop at stores that carry professional work attire with prices a post grad can afford such as JC Penney, Sears, or Kohl's. Remember, you don't need a ton of new outfits but a few key pieces that you can mix and match.
Good luck, post grad! When you look the part and know your stuff, you're sure to snag a job or go up the job ladder in no time.