Stick to the classics of the season - spring and summer are great for Stripes - try white / blue nautical ones from Splendid, JCrew, Gap, St. James or Petit Beateau. Buy a new one each spring to update shape and fabric but wear your old ones too, since classic stripes never go out of style.
Take a hint from Gwyneth's GOOP site and buy a classic trench. You'll own it forever and it adds instant, classic chic to jeans, your striped tee and flats. Invest in Burberry or try Banana Republic or Jcrew for a preppy twist on this forever staple.
Last tip for today - the leather jacket. This is definitely an investment piece but the right one can last a lifetime. Use your own personal life and taste to pick black / brown, hooded / motorcycle, studded / streamlined / drape collar... Spend some time and pick quality - you only need one.
More to come...