following作代詞時單復數同體，The following are/is 都可以，取決於後面的表語是單數還是復數。
詞典解釋：(the following) [TREATED AS SINGULAR OR PLURAL] What follows or comes next: 'the following are both grammatically correct sentences'
as follows 和 the following 是正確的用法。
The following are the tips that I would like to mention.
The tips that I would like to mention are as follows.
The tips that I would like to mention are the following.