The mistake of searching for random keywords is related to the bigger problem of not considering the broad topic while doing keyword research.
Do you find yourself in the scenario where you wait a few days between writing new blog posts and then suddenly start finding keywords on any random topic you can think of?
This is due to a lack of adequate pre-planning.
Before you conduct keyword research, you should devote some time to content planning. What is the broad topic you want to focus on in the next one or two months?
Once you have determined the broad topic, segregate this topic into its sub-topics that are large enough to accommodate individual blog posts.
This is also called the Cluster approach to blogging, where you create Pillar content on a broad topic.
Then you create individual posts on sub-topics and link to the pillar content. In the example of mobile accessories, this would imply creating pillar content on the broad topic of mobile accessories.
After this, you should create individual blog posts on sub-topics like mobile USB cable, mobile cases, mobile chargers, etc.
When you conduct keyword research using the cluster approach to content creation, you are much more likely to find targeted keywords around your chosen topic as compared to searching randomly.