To create the best possible personalization for future sequence it is recommended to first add leads to the campaign. Mainly because then you can see what type of data exists on the leads you are targeting. (The type of data will differ for different users and target groups.)
After you've added the leads. Export the data in a CSV file (see help article if you haven't done it before).
In the CSV file you get a good overview which datapoints are more useful for your campaign.
Be creative how you can create sentences around these. A good way to look at it is, how would you write an email being as tailored as possible just for one lead. From there we can then create these sentences in the Personalization Engine.
Please share your creativity with us, and don't hesitate to contact us if you want some help here.