Glassblowing

Glassblowing is one of the main ways to train crafting on a UIM.

All methods that involve buying supplies from charter ships will involve hopping worlds. To do this more easily, install the "World Hopper" plugin which provides shortcuts like Ctrl+Shift+Right to quick-hop to the next world (configurable). Disable the world switcher confirmation in the settings so that the keyboard shortcut will hop you to the next world without 

When starting out, the typical method is to buy buckets of sand and soda ash from the charter ship in Port Phasmatys, where a furnace is located to smelt those supplies into molten glass to make whatever your crafting level is the highest for and sell it back to the store or drop (selling to the shop is preferred if possible). I would recommend cutting gems from bags full of gems (mining stars) over this method because it is pretty slow and tedious.

With 77 magic and access to the lunar spellbook, the above method can be simplified by using the Superglass Make spell which converts buckets of sand + soda ash into molten glass (with a chance to create extra). This can be done at any charter ship shop since there's no need for a furnace. It is easy to go back to the normal spellbook since the lunar home teleport brings you to the astral altar where you switch back. On the lunar spellbook, the explorer's ring teleport to the Falador farm will put you near the Port Sarim charter ship.

I recommend an account build with 20 free inventory spaces (looting bag or deathbank your items) that can switch between doing this and some AFK activity.