There are a few techniques and "do"s & "don't"s that can increase e-mail opening and click rates:
1- Video. Studies have shown that e-mails with links to video have a higher rate of click throughs and conversion.
2- Images: there are conflicting studies and reports on using images. Although many argue that it's a good thing to add, I've noticed that our e-mail marketing click throughs increase when we have no images.
3- Keep the e-mail short.
4- Depending on your target and their habits, it is best to send e-mails on Tuesdays and Thursdays. Before noon or around 3PM. This info varies, you should experiment and see when you get the highest opening.
5- Send the same e-mail to people who did not open it, but change the subject line. Your platform should have a feature on this.
6- Avoid long subject lines.
As far as tools:
Infusionsoft has a good solution that combines CRM with e-mail marketing. But it has a horrific interface and it's expensive, although much cheaper than HubSpot.
Check out HubSpot's blog, they have great insight on e-mail marketing. Their CRM is free, by the way.