Assuming you are playing on a high difficulty level, #1 priority is to send out Curraghs to find other AIs and trade techs, hopefully before they swap everything themselves.
I do this on continents as well, trying to find the other continent.
Seafaring is incredibly helpful for allowing you to do this, and thus gain a tech lead or at least not get behind. But you must send the boats out, even without seafaring.
In my current continents, 70% water, deity map, I sent out suicide Curraghs across the ocean. Send out 2, pretty early, non seafaring race here. One found land, and in fact, the other continent, and the other 3AIs over there. They had a tech that AIs on my continent didnt. Ais on my continent had a tech they didnt. By buying these, swapping for other stuff, I was able to gain all the techs known to more than 1 AI, for a net cost of only several hundred gold. I went from knowing only 1 tech beyond my starting techs, to knowing 3/4 of the ancient age techs. This was essentially in return for the effort of 2 curraghs, for 30 shields.
Great library wouldve cost 600 shields to do a similar thing.
Also, because I was the only one in contact with all civs, the others only knew each other on the continent at the time, I was able to continue this tech brokering until the middle of the middle ages (when GL wouldve gone useless). I got about as much benefit from the couple curraghs as I wouldve from GL. And, there is no way I wouldve been able to get the GL.