Get your readers' attention by making better use of your subject line.
So, it's easy to use merge tags to start your newsletter, fill in the date or provide your address. But, you can do a lot more than say "Hey FNAME". You can use a merge tag in your subject line.
Let's say that you send out a weekly store update newsletter to all of your subscribers. But, you send it out on different days to different segments (2 days before a big sale to your "Premium Members", 1 day before for your "VIP Members" and day of for other subscribers. Your subject could read something like "*|MC:DATE|*, Big Savings Ahead"
Or maybe you like to send out special product alerts to some of your subscribers - stuff you know they would really like. Your subject line could get personal and say something like: Hey *|FNAME|*, you need this.
Here's another example, let's say that you have all of your users sign up for a How To Newsletter. And you get them to rank their own skill level in your signup form. So, not only can you segment by skill, you can also let them know that they are getting your Newbie How To newsletter. Got a project for everyone? Set your subject up to say something like *|GROUPSKILL|* Project Newsletter, so everyone can give it a try.
As you can see, there are lots of things you can do to personalized the subject line with Merge tags. But, here's the golden rule of Subject lines - You can't set up conditional statements or use dynamic merge tags. So, no If and If Else tags. A subject line just isn't the place for complicated code, like that. Feel free to use it in the body of your content, especially if you want to include content that works for one segment of your list, but not everyone.
Here's the big take away - Subject lines are a great place to get creative. But don't get complicated. Keep it simple, make it personal and no If and If else.
Note
If you're planning to post your campaign to Facebook or Twitter, don't use a Merge tag subject line. You won't be able to conceal your merge tag and there won't be any information for it to pull.