Gemming Guide
Right click a gem to open this window or press the "regrade item" button in your inventory and press the lunagem tab at the top.
NOTE: The 100% slot chance after the first 2 slots ONLY applies for Tier 3 (blue) Toughness and Resilience gems which slot into your leg and chest armor.
Once you upgrade out of catch-up gear, your goal should be to fill the slots with all T4 (pink gems).
For your other pieces of gear, consider using crafted lunagems or prestige lunascales (100% slot rate). A common strategy is to put the highest tier crafted gem in the first 2 slots (100% slot rate) and then use the prestige lunascales (100% slot rate at all times) for the remaining slots