IOS App Development are often an excellent way to turn your idea and start a promising career because the becoming an IOS developer is far more good than any other mobile applications developer, yes they are good but the payments in the IOS development is quite high nowadays which might change in the future but right now the iOS development is far more expensive as compared to the other developments.
So the very first thing is to get friendly with the iOS environment because if you want to develop some apps for iPhone the environment should be very friendly with you. The main things that we should be familiar with is:
1.how the screen looks like
2.how the segues are moved
3.how the app transition happen
4.how the permission pop-up looks like
This is required in order to understand the feel and polished look that Apple is trying to give in each application without that if the app is developed then it is not going to be a great app for sure. So, first of all familiarization with the iOS environment is much more important out there.
Once you'll get started with the familiarization and it's done then you can move on to the development phase in which the language which you might want to learn for the iOS app development is Swift but designing an iOS app might be a tricky process although you might be working in some company or like that but if you are looking for a freelancer the number one step is to design your app first not to code your app which means make sure that you've a rough sketch of your app before developing it.