Best of luck with your new android phone, I did exactly the same last year and switched from my iPhone to the galaxy S4..
It will seem strange to start with, a lot more questions for the phone your not used to seeing or dealing with, choices of what browser for things to open in, media players to choose from,warnings about what access apps have on your phone with scary terminology about what they control, but you will soon realise its just what the apps do on he iPhone just your not made aware so much of there content.. but after a few days and a small learning curve you will not go back, in fact if it wasn't for that my family all have iPads and I FaceTime a lot I'd ditch my annoying ipad for a Samsung tablet tomorrow..
A few essentials I found to ease the journey:
- choose a browser you like, opera for me but many like chrome..
- install swift key keyboard, good predictive text, the stock samsung was useless for me
- sort out what apps and widgets you might use and hide the rest
- install google hangouts for messages as it works better then the stock one and you can use it as a FaceTime/Skype substitute as well as working better with emoji
- turn off google now unless you think you will use it a lot as it drains power a bit
On the subject of that put the phone in power saving mode,
- Install keis on your pc to back up your phone like you do with iTunes
Unless you absolutely hate it, you will soon see the advantages come through over iOS and the larger screen with superior colours with be a joy to use,, my iPad mini retina looks dull and lifeless when comparing it to my s4 screen..
Have fun, persevere and enjoy..