Simple Mobile First @media queries

gistfile1.css

/* 
=============================
# Mobile First @media queries
=============================
 */

/* styles for iphone portrait go up here*/

/* Smartphones (landscape) ----------- */
@media only screen
and (min-width : 321px) {
/* styles */
}

/* iphone 5 landscape ---------------- */
@media only screen
and (min-width : 568px) {
/* styles */
}

/* iPads (portrait) ------------------ */
@media only screen
and (min-width : 768px) {
/* styles */
}

/* iPads (landscape) ---------------- */
@media only screen
and (min-width : 1024px) {
/* Styles */
} 

/* Desktops and laptops ------------- */
@media only screen
and (min-width : 1224px) {
/* Styles */
}

Keep in mind: styles cascade down as screen sizes increase