As a parent I try to say yes as much as possible. I look for ways to say yes. However you cannot avoid the need to say no. As Otis is mobile he is hearing it more than ever. He is probably hearing it a little too much. I re-read some of my Montessori texts and Montessori from the Start probably has the best description of how to say no.
I think at first it's important to remember that infants don't know what no means. Just by saying it, repeating it and getting louder or more urgent won't help. At this age you physically need to show your child what no means. This could be as simple as removing the forbidden item from the child's reach, line of sight or redirecting your child.
Lillard and Jessen (Montessori from the Start) refer to redirecting the child in a respectful manner.
If you child crawls or walks rapidly away from you, try not to swoop her up from behind into your arms. Instead, go around in front of her and stop her motion by facing her. You are then able to redirect her energies in a decisive and, at the same time respectful manner.
Because so often I see children (I possibly have done this myself) treat their child like a piece of clay, picking them up from behind, without any warning to redirect them.
By redirecting your child in this way, you are showing her that she is not a "lump of clay" to you; she is a developing person. You are respecting her as someone who must one day "turn herself around" and not expect "rescue from behind".
Another tip from Lillard and Jessen. Be consistent.
Redirect her behaviour every single time that that behaviour is inappropriate. Do not think that maybe this once you can let something go. You cannot. The child can only internalise firmness and an understanding of finality and limits in life from your consistency and your confindent manner in helping her.
And this wonderful quote
...the adult's role is to "teach children limits with love or the world will teach them without it."
This is the advice I need right now. Limits with love.