1. Ineffective Subject Lines. The subject line of your email is the most critical part, even more than the actual content of your email message. But why? The subject line is the first thing people see and directly influences them to open your email. You should be running tests and experiments on every campaign you send. It’s the only way to learn what works and what doesn’t work. Work to keep your subject lines under 50 characters and avoid buzzwords (“sale", “reminder”, "percent off”, “product”, “deal”). Why try and avoid buzzwords? It's because our inboxes are getting smarter. For example, if you use Gmail, you'll see that it works to automatically filter and place emails in different inbox sections ("promotional", "spam", etc). Having similar buzzwords to those spammy and promotional email messages can instantly place your email right into those respective sections.