Help for a highschool newbie

Hey monkeys, i have been a long time reader at WSO and from tomorrow my summer vacations are going to start and i am kind of trying to study trading. I have openend a demo account via GCI trading thingy and i wanna know how to use ( i mean what kind of commodities should i focus on) and if someone could provide me some tricks and tips about metatrader 4 and the market as a whole, that would be soo much helpful for me ( I will be attending university this september in UK, so i got plently of time to gain the experience)