Play at least one time on vanilla.
Fallout 4 is a great game with and without mods. Mods are here to enhance what mod authors enjoyed about the game or remove what they didn't.
How do you know what to enhance or alter if you've never played the game?
Set Up Your Testing Environment
Clear your reserve space. Start fresh by clearing the reserve of all mods and Creation Club Content for a fresh download of individual mods that you would like to test. If you're already starting fresh (that is: having never installed Creation Club Content or mods or are coming back to the game with a new install) then clearing your reserve space is not necessary.
Manage Your Saves
Turn off autosave, and do not use exit save or quicksave while testing. The game only stores three autosaves. Exit save and quicksave are overwritten each time you use them. You'll be able to keep up with your saves more easily if you manually save (create a hard save) each time. When exiting the game, go to a different cell first so that when you re-enter the game, the data will load in properly, then exit by opening the Pip-boy first.
Create a Series of Clean Saves
When the game loads create a series of saves at intervals of sixty seconds. PS4 Players should be able to rename these saves. Xbox players will need to manage them by keeping up with the timestamp on the save. Xbox players also have the ability to use Cheat Terminal to rename their character to keep up with it that way.
Be advised that using Cheat Terminal will not allow you to have a true clean save nor will you be able to report any bugs to mod authors should they be encountered, especially if you have used cheats during your save or have teleported around things instead of going through the appropriate quests or triggers.
Keep up with what you download
The Load Order Framework is here for a reason. It gives you a way to manage your load order outside of the Xbox in-game mod manager. Copy the blank Framework template to your Google Drive, use the first tab to make additional templates for your testing purposes. Use it to plan and test your load order.
Read the Descriptions
Just as with planning your load order for actual play, plan each test by ensuring you've installed a mod at the appropriate time and with any dependencies. Does it need to be installed before or after the Prologue? Does it require another mod to function properly? Just as with normal gameplay with mods, waiting too long for quests to run may cause the mod you're testing to break if it needs a quest that runs and stops before you got your hair did.
Know What Mods Do Before Committing to a Real Game
Enable and test mods individually before testing altogether. You need to know what a mod does in its vanilla state before you can add others.
Asking on the Parent Server can help you save some time; however, there are over 13,000 mods on Bethesda.net for Xbox with new mods added daily. There's not a way for one individual to know what everything does. We're here to help and give you a community to support you when you're frustrated, but you still need to see for yourself what it does so you can judge whether or not you want to keep it in a main save.
A Vault Dweller's Load Order Survival Guide: Test Characters and You - Why They Matter
Load Order Glossary - Survive Load Order Disorder by knowing what a mod author means in their description.