I generally use a 1230AP with 2.2dbi horn antenna for an internal site survey. I try and site the AP as near to the proposed locations as I can get it and ensure the antenna are vertical. For a client either a 350 PCMCIA or 802.11a/b/g with latest client software.
However....a lot depends on what sort of WLAN you're surveying for. Is is PC clients, building to building, etc, etc.
You could check the ff link for your refernce:
Implementing different antenna could improve the coverage and performance.
There is no definitive answer to your question. There is no "standard" height as this will vary from site to site. The angle of antenna will also depend on the radio propagation required. A detailed site survey will always determine both your requirements.