It's more about type of your business.
In terms of B2B there is only one thing which helps startups live - is sales. Direct sales, conf. sales. Until you reach solid revenue content marketing efforts can be useless.
And it's also related to guest blogging.
In terms of B2C. Yes, guestblogging is a good strategy.
Some things you should know:
1) You need to guestblog before the launch. Create landing page with wait-list which aggregates emails and start to post on other resources to attract leads.
2) Use 2 types of sites - highly specific blogs and average specific blogs.
Highly specific blogs are your industry blogs (for example, on marketing, design). It helps to generate more targeted traffic. But once you reach a limit in this niche, you need to go further.
Average specific blogs. For instance, it.s Entrepreneur, Inc, Forbes. It's less targeted traffic. But! There is a much more readers. And it's a good opportunity to get new customers.
Always try to combine guest blogging on these types of blogs. NEVER focus only on industry blogs. Because there is a risk of writing for the same audience again, again and again.
3) Try to combine your guestposts with live speaking. Become speaker on some local events. Speak on your business topic and make alluions to your posts. It should sound like - "BTW, We also wrote about it in our post at Entrepreneur". You can also add this allusions as links in your followup letters.
It helps to generate more virality to your posts - drive more attention to you and your startup.
4) Last step is a cross-market distribution. But it's for mature stages of your startup.
HOWEVER! I should say it again...
...that for any early startup there is only one crucial thing is SALES.
You can make guestblogging. It's an effective strategy. But for early stage startup is not more than 5% of your overall efforts.
Rest 95% - is development and sales.