I can throw out two tips for Fate Core GMs: always throw out a sparing number of environmental or situational Aspects, usually written on Index Cards or noted on the Map Layer (for Roll20). There is the setting's Current Issue and Impending Issue, but you can make up others. Encourage players to Create a (new) Advantage (or exploit an existing Advantage), the roll-result chart is slightly different for each of these. It is an under-used Action. So, if a forest has Ground Full of Sticks , obviously the cave-man PCs can rub two of them together and Create an Advantage, Fire! Unless they fail to, or if they roll hideously they set their furs on fire which the opposition can Compel! Also, players should not talk about Invoking stuff until they see what their initial Fate Dice roll is. If the roll isn't good enough, then the PCs and the GM can spend Fate Points to bring in Aspects (good for a +2 or Re-roll). The Fate Core frame-work is loose. Coming out of my past, I see it as downright innumerate! But you can make it live. Keep your descriptions short but be dramatic. Offer more details about sights, sounds, smells only if characters investigate (the players ask the right questions). In Combat, look for ways to combine use of Aspects, Boosts and the Teamwork rule (+1 for every person helping who has at least 1 in the Skill, to a reasonable limit, but they share in the problems if it fails) to give the PCs a devastating wallop. The NPCs may return the favour. Always describe in story terms and you may end up with amazing combat and other situations.
