Assess your competences
As a job seeker, it's important to know and be able to explain what you are capable of. You must make sure that it's clear why an employer should hire you.
You have worked on and practiced your competences by e.g. studying at university. You have learned some skills that are specific to your degree, but you have also been tauhgt to work in a certain way, what we call "general academic competences." Your way of working is something you share with others who have also studied at the university, and especially within the same faculty as you. And finally, you are good at a lot of things that are personal to you. All these types of competences are important - also when you apply for a job.
Learn how to assess and describe your competences.
Describe the value you can create
You need to make it clear for the organisation, why they shoudl hire you. That is your job and applies to when you write an application for a solicited ad, but especially for an unsolicited job.
Being able to describe your competences and which tasks you can solve is good. But it's really a plus if you can to explain to them, which value you would be able to create in their company, if they hire you. There is a difference between “I am able to…” and “If you hire me, you will get…”

So, it's something employers want. But it's often easier said than done – it takes practice, just as it takes thought and practice to explain which competences you have gained throughout your study.
How to find and explain the value you can create

The value you can create is of course also dependent on what the company needs. Now, this is where researching the company is very important. If they aren't facing any challenges or need any help in the given area, they might not see the sense in the value you want to create.