(8) If the item has a blue symbol and says "intricate" you should usually deconstruct it. (7) If the item has a gold money bag symbol and says "ornate" in the description, you likely want to sell it. Or wear them! At early levels, these are often the highest quality items you can obtain to wear for your personal use. (6) If green, you can deconstruct, learn the trait at a crafting table (if the item has one), sell to any npc for gold, or you can try to sell in a guild store. (You can just drag outside of the inventory window, or right click.) but if you run out of room in your inventory before you can get to a crafting table, these are the first items you should get rid of. If white/low value, deconstruct unless you desperately need the gold. (5) If items are white/high value, sell them. If forced to choose, always keep gold>purple>blue>green>white. (4) Be aware that there is a color-coded value system for materials and motifs. (4) As you collect motifs/diagrams/recipes/patterns/etc., learn or sell them as soon as you can, so they won't clutter your inventory. You may want to focus on materials for the crafts most important to you. Start by considering which crafts you want to focus on. (3) If you can't, or don't want to add ESO+, but you want to craft, you will need to be very strategic with your inventory.
(2) Assuming #1 is correct, are you interested in crafting? If so, consider adding ESO+ if you can afford it. (1) I'm guessing you don't have ESO+, or your materials would automatically flow into your unlimited crafting bag.