This is a really excellent post on how to go about raising follow-on funding from First Round's Bill Trenchard and Brett Berson. 

FirstCapital helps companies raise growth capital funding, and we see a lot of these issues, all the time. Key pieces of advice from this article that stood out for me: 

1. Never run a process half-heartedly. You are either fundraising or you are not. Don't get sucked into a series of conversations that never really go anywhere;

2. Inbound investor interest, especially if it is not from a partner, is not necessarily an indication of demand. It is probably just someone doing their job, researching the market;

3. Markets change. Just because your last round was easy doesn't mean this one will be;

4. There are few things more important than your credibility as a founder. If you lose this (eg through overselling) it's almost impossible to regain, and this will kill the process;

5. Research and target the right individuals and the right investors, and then run the conversations in parallel: scarcity, competition and momentum creates demand.

I'd highly recommend you reading the whole article, it's packed with thoughtful, real world advice for entrepreneurs.