Hi,
Havent really bid on technical writing before but used to do if for a living many years ago, but at that time it was procedures for implantable pacemaker assembly and test.
Being a Freelancer offering services related to electronics design, PCB layout, and Arduino I'm both a user and critic of the available documentation.
It is so important to identify the taget audience, and this is not a judgement, but you can go for the data (reviews etc) supplied by Adafruit, Pololu and Sparkfun and compare them to the offerings of "instructables" to gauge the differences in approaches.
A good review appears to be testing, experimentation and commentry by the author with pics etc. This (justifiably) gives the product credibility especially if accompanied with worked examples.
I have to admit being impressed with the Sparkfun and Adafruit offerings and the quality and their offerings.
Happy to chat and good luck with your search.
James Harrison-Smith
Infonics (Sydney)