Unless you're collecting friends for the 50 Friends Quest there's no point on having people on your friend list if they're not playing the game anymore. So, in order to maximize your daily energy claim you should, once in a while, check if your friends are still playing considering these factors:

• How long was the last login
• The trainer level
• Real world situations like the Holiday Seasons

The game already give us an awesome tool that eases up this task.

When you go over to your friends list in the Social button at the bottom of the screen, you can see for how long that person hasn't been active.

That alone it's a good indicator for you, but do keep in mind to consider if you're currently in a exceptional week like the week before and after Christmas or New Year's Eve because on those particular times players tend to play less.

• Now, considering the factors we've talked about at the beginning, select the person you wish to no longer be friend's with.
• Tap Delete Friend and that's it. Now you can invite new people to be your friend!

By having an active friends list you'll increase your changes to earn the maximum daily Energy from your friends!