Read the job description/understand the advertisement
Always go through the job description of the position you are applying for. Understanding the job description and the advertisement is the key to the whole process. Your cover letter should be designed with the vacancy in mind, so it is important that you are able to analyze the advertisement, and make the correct deductions from it.
Mention skills according to Job title
Do not mention your computer skills in the first paragraph if the job title is about another field (other than computer). For example, a position for sales assistant will be assessed on how much experience you have in the field of sales, not computer. Most advertisements of jobs clearly mention the job title as well without going into details of the job description.. This will give you an idea of how the company sees it. If the company has asked for specialties in the field other than your core job experience, then you should know that the letter must include computer skills.
Mention computer skills right after your core skills
It is wise to mention your computer skills right after your core skills. Since, most of the positions today require computer skills, the employer wants to know if the potential employee is capable of carrying out different tasks of the job that are not possible without the use of computer. For instance, a sales assistant should be well versed in using Microsoft Excel and sales tracking sheets (both by using software and MS Excel). In such jobs, computer skills become crucial. So, mention all these skills briefly right after you explain your core job skills (whatever that may be).