A few things to keep in mind while chaining:
- The Poké Radar cannot be used while using the Bicycle or Roller Skates.
- It cannot be used in a friend safari.
- If you flee it breaks your chain(though you beat the Noctowl)
You might want to stay away from patches of grass very close to you after each encounter and do not go to the edge of the field, that will most likely break your chain unless you are really lucky.
Always go to the patch that shakes the most, however, in X/Y they made it so you can encounter other Pokemon even if you are doing everything how you are supposed to so you might be just unlucky as well.
Going into the right grass patch is easily the hardest part of chaining so just practice more if that is the problem.
Hope I helped. :]