Invite

To join a private tracker you either have to receive an invite, sign up through an open registration period, or join through an application.

Invites From Members
There are two ways to properly get an invite to a private tracker, one way to get invited is from a current member. The member has to have invite credits on their account as well as privileges to send them. Depending on the tracker, invite credits can either be received on a monthly basis, purchased with bonus points, or received as a prize from contests.

Just because a user has invite credits doesn't mean they can be sent. Some trackers restrict invite sending to certain user classes, and also disable them for normal users when the user limit has been reached.

It is important to know that you should not ask to buy or trade invites as well as receive them from public giveaways. This is a huge offense on most trackers and can get you as well as your entire invite tree disabled.

Invites From Staff
On many tracker's class restricted forums (forums that you must have at least a certain user class to view) there are official recruitment threads where staff are offering invites. These threads will tell you about the tracker, state and state some requirements for you to be invited. If you have the requirements, you send them a message and they will send you an invite. Common requirements are:
 * Have been a member for x amount of time. Usually achieved if you can see the post.
 * Currently no warnings on your account
 * Proof of 2-3 accounts on other trackers. Usually provide links to your profile on other trackers which prove you are a good member. This doesn't necessarily mean you have to have a lot of uploaded credit, they want to see that you can maintain good standings, community participation and uploading are a bonus.
 * Not have ever had an account on the tracker
 * Not be from a banned country
 * Specific subject requirements to make sure you can read. If they say "put your email in the subject" and you don't put your email in the subject, they're going to skip right over your message.

Illegal Invites
Users most take care to not receive invites in a way that breaks tracker rules. Most trackers have strict policies against any invites purchased, received from public giveaways, or traded. If an invite is received through any of these means then there is a big risk of having the account disabled, anyone the account has invited, the invitee and anyone they've invited.

After you are disabled on a tracker, you are never allowed to have an account there again unless you work things out with the staff. Your IP address is logged and many times trackers will share this IP address and a group of trackers will disable your account.