Most of the time your iPhone can get a good GPS signal in <10 seconds. But if you're having issues, you can try the following:
- Make sure you're outside; being indoors can degrade the accuracy of your phone's GPS.
- Let Slopes get a good GPS fix before you turn off cell data or wifi as those can speed up the acquisition process.
- Make sure Airplane and Low Power modes are off as they do affect the accuracy of your GPS. Turn off cell data instead.
- Try keeping your phone in a different location. Some clothing materials really hurt GPS reception, or you might have it under too many layers.
- Head to the settings for Slopes (under About tab), go into Location Services, and toggle access off and then back on.
- Worst case, reboot your phone. This is rare, but I've seen it fix poor GPS reception issues.
If you're running Slopes via an Apple Watch, it is highly recommended you keep your phone with you when you ride to improve GPS accuracy.