From fairest creatures we desire increase,
That thereby beauty's rose might never die,
But as the riper should by time decease,
His tender heir might bear his memory:
But thou contracted to thine own bright eyes,
Feed'st thy light's flame with self-substantial fuel,
Making a famine where abundance lies,
Thy self thy foe, to thy sweet self too cruel:
Thou that art now the world's fresh ornament,
And only herald to the gaudy spring,
Within thine own bud buriest thy content,
And, tender churl, mak'st waste in niggarding:
Pity the world, or else this glutton be,
To eat the world's due, by the grave and thee.

As the opening sonnet of the sequence, this one obviously has especial importance. It appears to look both before and after, into the future and the past. It sets the tone for the following group of so called 'procreation' sonnets 1-17. In addition, many of the compelling ideas of the later sonnets are first sketched out here - the youth's beauty, his vulnerability in the face of time's cruel processes, his potential for harm, to the world, and to himself, (perhaps also to his lovers), nature's beauty, which is dull in comparison to his, the threat of disease and cankers, the folly of being miserly, the need to see the world in a larger sense than through one's own restricted vision.

. From fairest creatures we desire increase, fairest creatures = all living things that are beautiful. increase = procreation, offspring. A reference also to the increase of the harvest, by which one seed of corn becomes many
2. That thereby beauty's rose might never die, thereby = in that way, by that means. beauty's rose The rose was symbolic of all things beautiful. By reproducing itself it could, in a sense, become immortal.
3. But as the riper should by time decease, riper = older, more mature, (person, plant, thing) more ready for harvesting.