I just thought I'd add in my two cents, since I too had much trouble getting things to work by following the instructions ("Setting Up Raspberry Pi as a WiFi Access Point" & "Onion Pi").
In my case, for reasons I haven't determined, the static IP address I assigned to wlan0 (192.168.42.1) kept "disappearing" before the dhcpd server started up, which led to it failing to start up, yada yada.
In my case, I followed the tutorial instructions verbatim, which is probably the root cause of my issues, at least according to some of the forum responses I've read.
FYI - my Onion Pi is wire-connected to a router that automatically assigns local IP addresses (192.168.0.XXX) via DHCP to attached devices, like my Onion Pi. The router, in turn, is connected to the cable modem, the IP address of which is assigned by the cable company.
My kludge (I won't dignify it by calling it a "fix") was to add an explicit "ifconfig" statement to the "start" and "restart" cases in the shell script: /etc/init.d/isc-dhcp-server.
One obvious problem with this "solution" is that it will mysteriously disappear should I ever run an update to the isc-dhcp-server Linux package which would likely overwrite that start-up script. The "sudden", resulting failure months from now (you know, Alzheimer's and all that) is certain to be a head-scratcher, for sure!