Are you a paper committee paper or journal associate editor (AE) who want to increase the likelihood of reviewers responding positively to your invitations?
Here are some tips based on my own experience:
Instead of a machine-generated generic email, craft a custom message telling the candidate reviewer why you think they are a good fit for the paper, such as their background respect to the topic or specific components of the paper.
You should have this information already when deciding to invite that particular reviewer.
Add some personal greetings such as if the reviewer has a recent job change or life event, a new paper, or someone you both know, which could be found on their social media or personal website.
Do so particularly if you know the reviewer (or someone close to them like their collaborator/advisor) personally.
If you already read the paper, provide some estimation of the time commitment required for reviewing the paper, e.g., “I think it will take you about 2 hours to review this paper”.
If you have accepted review requests from that reviewer in the past, mention this as well as a hint of reciprocity.
This is another reason to accept review requests if you have the bandwidth.