The more levels you upgrade the higher level items that you can start crafting. Skill trainers only allow you to upgrade to level 10 where you will then have 2 other options to continue upgrading your craft level.
Learn from other players (recommended)
You can find crafters of higher levels on the community craft list or by shouts in Atlantica online gold game that are constantly being sent by others. You have the ability to teach skills to others also by shouting in the world chat also.
High level crafters will get bonus points for teaching your crafting levels and you will also get points for teaching others also. This is a win win situation for everyone. When you find someone that you want to teach crafting or you want to learn crafting from you must be lower level than them.
If this is the case then you can add them to friends list and they/you can click actions in the whisper window of your newly added friend and click actions--> share info. Then you can locate what you want to teach or the other person will find what you need to learn and then share the information with you.
Wandering Crafting NPC's (Last Resort)
There are wandering NPC's that you can learn skill levels from. You will have to pay money for each upgrade from them which becomes very inconvenient if you have a lot of levels that you need to upgrade to. Another inconvenience is that its very difficult to locate these NCP's much less the one that you need to find for your particular craft upgrade.
If you are the highest level in the game for a certain area you are limited to upgrading your craft this way. But more often than not you will not be and you can upgrade free and easy from someones else's work.
Once you hit level 10 go out there and start teaching crafting to gain points... use world chat as much as you can also, it only costs 1k gold so its cheap!