A personal brand is something you work on many levels to build, first by getting to know yourself better and then by understanding what you want to communicate to your target audience before even opening your mouth (or posting in social media). Simply put: it is a vision. When you do open your mouth, it should become all about the message you’re trying to transmit, not about hard-selling yourself.
Certainly, self-promotion is an extremely important part of building your brand because if no one knows of your accomplishments or the company you work for, then how are they going to do business with you?
It also seems that the biggest factor separating personal branding from shameless self-promotion is value.
If a person provides value with his/her content, then all the self-promotion is justified because people will benefit from the content.
Once you really understand your values and know what you want your brand image to be, then you will understand that overpromoting your services will hurt your brand. You must align your communication and overall message with your target audience, not only the message.
Don’t feel that it is wrong to provide information about the content that you provide. Just make sure that it is targeted to the right audience and be personal while doing it.