What Character are you playing?
There are various crafting gathering skills that are recommended for each character. I ignored this at my peril and trained in random ones that I thought were cool - oops.
Luckily you can 'unlearn' skills and train in new ones. Then it's a matter of
** Sending your companions on crating material gathering missions.
** Gathering the same crafting materials in game as you explore the planets.
** Buying crafting materials on the Galactic Market
** Tasking your companions to build the items that you have blueprints for.
** You can buy blueprints form your crafting vendors or on the Galactic Market.
** To increase your core crafting skill build the more challenging items on your list (Check out their colour coded difficulty rating)
** To improve on the quality of the items that you have built, "use reverse engineering" by doing this you stand the chance of learning a blueprint for an improved version of the item that you created.
For a more indepth guide have a look here! (However the one small section on 'mods'may be outdated.)http://www.starwarsmmolevelingguide.com/crafting-guide/
All the best,