As I mention in [my answer][1] to the question on [What research methods can I use to create personas?][2], some key elements to keeping the persona valid and relevant include:

 - **state your research goals** before you start so that the persona can be kept relevant to your goals
 - **define how you will use personas** so that you can ensure your personas include the relevant detail and content to move directly to the next phase of the process
 - **interview real users** where possible
 - **undertake ethnographic research** where possible to get context for your content
 - **review as you go** so that you can assess the persona against your goals, and are working towards the achievements you set out to meet, and be prepared to adapt if necessary
 - **keep it real** by always following up on information that may be second hand research such as that from proto personas
 - **avoid [bullshit personas][3]** at all costs
 - **make it collaborative** so that everyone has input, and gets a chance to have their say. If everyone takes the journey together, then everyone can see the information has a history and a source, and can be used as evidence, rather than some black box of information gathered by an outside agency for example.

**Just keep the bs out of the persona** and remember - **Personas are not just an artifact**

See the above linked answer for more detail on each item above and a handful of excellent references on personas.


  [1]: http://ux.stackexchange.com/a/21916/6046
  [2]: http://ux.stackexchange.com/questions/21891/what-research-methods-can-i-use-to-create-personas
  [3]: http://avoidbspersonas.com/
  [4]: http://www.thinkui.co.uk/2012/06/what-research-methods-can-one-use-to-create-personas/