The absolute basics to grinding out Weaponsmithing.
The only prerequisite to Weaponsmithing is Engineering IV in the Artisan
tree, a general Crafting
tool, and a weapon, droid, and general tool. Later on you will need a Crafting
droid or Crafting
station to make some items. You can make melee and ranged weapons (of course), as well as mines, grenades, and heavy weapons such as Launcher Pistols, which Commandos need for heavy weapon experience to start.
Grinding out Surveying IV first helps you find the materials you need faster and has the added bonus of gathering materials for your crafting grind later. When surveying, get the materials you will need later such as steel (lots), iron, fiberplast, polymer, gems, copper, etc. When grinding, quality doesn't matter.
Now, on to the grind...
Visit a cantina before you start. Practice mode and Entertainer
buffs will significantly improve the xp earned per item crafted. Make general crafting tools in practice mode until you have Engineering IV and Novice Weaponsmith.
Train Novice Weaponsmith and find something to grind without having to make multiple components to make an item. That is, make one item over and over in practice mode until you're Master.
Pick one of the following and go either Intermediate Melee, Ranged, or Munitions I. Take that tree all the way to IV to increase your xp cap for weapon crafting and unlock components that provide more xp.
Every time you go to the next tier, change to a new recipe for better xp. Once you are at IV, make an item from that level to grind out the rest of your xp, all the way to Master. Now you have to find quality materials to make quality weapons; but that's another guide.