It took me a thousand games until I realized the value of consumables. I still recommend staying away from the 250g elixirs until you've filled all your equipment slots. If you're soloing top with teleport, make sure you have two wards to survive the entire duration of the time your teleport is inactive. After your second ward expires, go back. THESE ITEMS PAY FOR THEMSELVES. If you're a caster with no real lifesteal/spell vamp/regen, stack up on HP pots. Look at my Brand replay. How many times I did buy pots? I must have used 20+. If you have empty slots and a little gold, use it. For 1.5 minion kills, an HP pot means the difference between being sent back home or staying in lane. Additional laning power is easily made up in an HP pot's cost. You'll farm better in the long run. As you approach mid/end-game, pick up 5 wards. I don't care if it's 375g. Get it. Light the map up like a cherry tree. Ward dragon. Ward blue. Ward the river... four times. Two up top, two on bot, including all the choke points. You should know where their team is at all times. If your team does this, you should essentially eliminate fog of war. A single kill is worth an entire stack of one player's wards for your team.
THIS STUFF PAYS FOR ITSELF. GET IT EARLY. GET IT OFTEN.
You cannot effectively control your lane without at least one ward exposing your flank. Ward your blind spot, stack health pots. Collect win.