Earn XP from Owning Games:
1-9 games: 100xp +5xp per game
10-24 games: 150xp +3.33xp per 10 above
25-49 games: 150xp + 2xp per game
50-99 games: 175xp + 1.5xp per game
100-499 games: 250xp + 0.75xp per game
500-2000+ games: Base xp seems to be gone only 1xp per game added

Earn XP with Crafting Badges:
The fastest way to level up is with Trading Card Sets.
You earn 100 XP per set you Craft into a Badge.
Trading Set of Cards can be Crafted x5 or a MAX of 500 XP to be earned.
Foil Trading Set of Cards can only be Crafted once for 100 XP.

Earn XP in Other Ways:
It is totally possible to reach a Level 10 (1000 XP) without Crafting any Trading Cards! Earn other XP by participating in Holiday Sells, get 50 XP for each Year of Service and Community Events!