How much or IF your rank rises or falls is mainly based on the rank of the opponents you beat as long as you are an active player. You move up half the distance between your rank and the person's you defeat, so the higher ranked your opponent is the further you will move up the Ladder if you win the match.
In other words, you can have ten wins in a row, but if your opponents were all ranked close to or behind you your actual Ladder rank will not improve much. However, playing lower ranked opponents can increase other ratings such as the win percentage and skill rating, so there are still benefits to your overall status.
When someone who is ranked below you wins a match and that player's new rank is above yours, you will slide down one rank on the Ladder. On a very large and active Ladder, this movement can cause a substantial drop in rank even after only one a short period of inactivity.