Are you using anything to track your engagement? I like a Chrome plug in called Socialbro. I use other tools as well but this one has an easy interface and gets me an idea of what is going on quickly. You are more likely to get responses at certain times. Theres also another plug in I would suggest called Buffer you can use to schedule them at optimal times for the highest reach. The more you know about your audience the more you can entice them with things they'd like to reply to or retweet. If you dont already, I would use bit.ly for links as this way you can measure the amount of interest in a subject by how many clicks you get. Another tip to is that surprisingly, your promotional tweets should only make up 5-15% of your total. I've read several blogs on the subject and the consensus is that similarly to how we 'turn off' to ads we also turn off to accounts who only do self promotion. Engaging works best for me when I just have really natural conversations with people. It seems counterintuative, but you'd be surprised at how those people come back when they do
need something because they remember my comment on that article they posted... I hope some of that helps.