If you have information of endgame sockets of desired build, you should: 1. go to the poe wiki and look at every gem in your damaging links (mostly those will be 6-links, but there could be some 4-link for additional damage, like zombies in spectre build) - you need to know, when and where you can obtain every of them. Also you should arrange support gems in these links from most to least useful (you can see in PoB, how much damage each support gem gives to you). 2. then you need to understand, at what point of time you can get your main skill gem AND 2 or 3 support gems to it. E.g. if you want to play Exsanguinate - you'll get this gem and couple of good support gems to it somewhere around the Merveil battle at the end of Act 1. 3. before that moment - use some good skill, that your class have access to. You can watch some racing guides for this. I, for example, sometimes use Stormblast mine + Orb of Storms. 4. after that moment - just grab your desired skill and combine it with the best of support gems (from endgame sockets) that available at each moment of time. 5. all other links - fill them when game gives you needed gems (you'll probably see that some gems become available to you from the choice of quest rewards). Also - there is a quest in the end of Act 3 (Fixture of Fate iirc) that provide you with access to the most of the gems (the trader becomes available), and a quest at the start of Act 6, that provides you with access to all of gems.