Tips On How To Pick Certain Fruits

I swear I have to ask this question from time to time because I legit do not know. I love love love fruit of all kinds, so I'm constantly buying it even thought half the time I don't know how? I bought both oranges and grapefruit the other day and just blindly grabbed a few of both...

So my question is, HOW DO YOU pick them? Are we looking for softness, more orange, less orange, I just want to know which ones are sweeter?