do some home work first..if you are serious interested about
advanced scanning techniques: understand the tool first, you are using!
Tweaking a little bit the default settings will be much
more silent in many cases (e.g. nmap timing & scanflag settings). But if you are really serious testing just a couple of specific devices, go for a fully customizable scanner, like
hping, unicornscan or just use the scapy python library and create your own fully custom scanner with a couple lines of code!
Highly recommended book: NMAP Handbook (really great,
even for experienced nmap users!)
Amazon.com: Nmap Network Scanning: The Official Nmap Project Guide to Network Discovery and Security Scanning (9780979958717): Gordon Fyodor Lyon: Books
Also don't forget, if you are looking for a real serious blackbox pentest, what you mostly need: hands-on experience, imagination, time & passion ;-)