When you are writing a more general recommendation, you should still ask the subject of your letter to outline their targets for employment. Ask them for an example or two of jobs they are applying for. Also ask them to share their most marketable assets for that type of work, especially ones you may have observed in your relationship with the person you are recommending.
The more information you have about the jobs or types of jobs the candidate is applying for, the more effective your recommendation can be.