If you are doing yourself;
1. Significant time investment for potentially very limited return. You will need to map all your key; I call it 'Yellow Book' contacts who you wish to target (it's very much a sales process), who you want to engage. Best way to do this is build a CRM like process to target journalists and get on their radar. Then work to engage, nurture and build relationships with them. Unless your brand has a significant angle to the market, your potential for coverage is minimal, or the impact of the odd placement you can get is minimal. It depends on your stage of growth but I'd focus on other levers if at small scale. It won't drive revenue.
2. If you are getting to scale you can hire a dedicated Comms & PR hire. But don't assume it's a revenue generation hire. It should be regarded as a hire for brand development. In previous companies I've seen good and bad, bad is someone who doesn't do a great deal, writes the odd press release and distributes it to PRNewswire.
3. You can distribute to PRNewswire if managing yourself for releases about your product and announcements. It costs circa £500 - £1,000+. Great for vanity metrics to show your CEO - will be some made up 15,000 views or something. What it means is highly negligible.
If you are using an agency;
1. Manage them with an iron fist. The second the pitching process is over and they are onboard. Natural sloppiness will ensue, there is a great peak of excitement about all the great coverage they'll generate and soon that will unravel. You have to give them clear direction, agreement on what you see as good outcomes. Do you want trade press, do you want news hijacking, research reports (all CEO's will say we want to be in the FT etc - for most brands it's somewhat unrealistic so be careful how you judge "success".
2. Be careful with agencies on minimum retainer. You will get good engagement at first but as soon as the agency stops seeing you as an upsell/ cross- sell opportunity you will soon see their interest slow down and outputs decrease. You have to be clear about the hours / minimum retainer spend to ensure your account team are working on the right things.
3. When I say you need to be clear. You need to 10X your clarity on brand narrative, your positioning and market positioning (and communicate over and over and over) as most agencies will not be clear about what you do and fail to sell you effectively to the press. You need to use them to leverage an angle that will help cut through into a topic that is societal (even if tech) and spin your product / solution into something more than features. This is the only way to even contemplate getting coverage outside of trade press.
I could go on but this foundational view will help your thought process.