Don't use Twitter for Spamming anyone

You may not use the Twitter service for the purpose of spamming anyone. What constitutes “spamming” will evolve as twitter respond to new tricks and tactics by spammers. Some of the factors that twitter take into account when determining what conduct is considered to be spamming are:

• If you have followed a large amount of users in a short amount of time;
• If you have followed and unfollowed people in a short time period, particularly by automated means (aggressive follower churn);
• If you repeatedly follow and unfollow people, whether to build followers or to garner more attention for your profile;
• If you have a small number of followers compared to the amount of people you are following;
• If your updates consist mainly of links, and not personal updates;
• If you post misleading links;
• If a large number of people are blocking you;
• The number of spam complaints that have been filed against you;
• If you post duplicate content over multiple accounts or multiple duplicate updates on one account;
• If you post multiple unrelated updates to a topic using #;
• If you post multiple unrelated updates to a trending or popular topic;
• If you send large numbers of duplicate @replies or mentions;
• If you send large numbers of unsolicited @replies or mentions in an attempt to spam a service or link;
• If you add a large number of unrelated users to lists in an attempt to spam a service or link;
• If you repeatedly post other users' Tweets as your own;
• If you have attempted to "sell" followers, particularly through tactics considered aggressive following or follower churn;
• Creating or purchasing accounts in order to gain followers;
• Using or promoting third-party sites that claim to get you more followers (such as follower trains, sites promising "more followers fast," or any other site that offers to automatically add followers to your account);
• If you create false or misleading Points of Interest;
• If you create Points of Interest to namesquat or spam.

Reference: Twitter.com