Hello @Farhan_Rasheed_Tragg first of all please use only English standard language to ask any question to us. At this time we translated your above question. Please try to speak English instead of other languages.
Answer: It depends on your expertise, which thing you know better than others such as Android, Smartphone hardware problems, Software issues, Software troubleshooting, WordPress etc. There are numerous things on which you can start writing to promote your business. It's up to you, first research then implementation then recommend to others.