There is no good way but A good practice to share unfortunate news is to always look them in the eyes and tell them the truth. Have your reasons ready to explain and expect a debate. You may find out your reasons actually involve you and what you want rather than it is them and what they can do to rectify things. Talk to the parents first, then talk to the player. If the parents don't want you to tell them it of course is their child, their choice.
Many times the skill level of the player is not measuring up to your demands and it is easier in your eyes to replace rather than work to improve the player. Keep this in mind when you drop the bomb that you don't want to take the time but would rather have a turn key player somebody else has prepared. At that time you may need to question yourself "Is this for me or for the kids?" Every team, even international status teams, have players with flaws in c comparison to other quality teammates. There will always be a king of the hill and a player in the cellar. Be sure of your decision before you make it. Some kids simply don't have the physical ability to execute at a higher level. Be sure to tell them why they are not coming back so they can work on the off season to hone their skills for another team. That's right, they'll be preparing to play against you.
If you sense the sarcasm in the above paragraph it's because I struggle with any club getting ready to dismiss a player if she's already shown you she wants to be part of the team. Unless a physical issue is present or problem with personality issues on and off the field make it too challenging, coaches should really be ready for what is next before cutting a player.
If all you are doing is notifying players that showed up for an open tryout then of course a phone call or card should suffice.
