First, your speed, if you are a beginner lash artist choose a glue with a slower drying time such as 2-3s as this will allow you to have more time to attach and adjust the extension correctly to the natural eyelash. The curing time of the glue you are using won’t determine how good of an artist you are, so please don’t buy the super fast glue just because you think that will make your work better or speed things up. It will only cause you headaches and unhappy clients because it will more likely to dry before you can reach the natural lash with the extension anyway, so if you are a beginner please choose a suitable glue with a bit slower drying time, don't forget that lashes are art and it takes time to do them correctly.
When it comes to application I always recommend for beginners to first isolate the natural lash and then pick up the glue and not the other way round, why ? Because if you pick up the glue before you isolate, that glue will start curing while you are trying to isolate the natural lash, which means it’s more likely gonna be at least half cured when you reach the natural lash. If you are a bit more experienced and you are confident in your skills, you can choose a faster drying glue. I personally like to use a 1 second drying time glue with a thin consistency.
The second thing to consider is the room conditions. If your room is hot and humid, choose a slower drying glue ( 2-3 seconds ) and if your room is cool and dry, choose a faster glue ( 0.5 - 1 second ) I will explain this in depth in my Maximum Retention E-book.