The most probable seeding will be as follows:
Heads of group: Top rated teams (according to FIFA classification, plus the results of the last 3 World Cups) + the host:
RSA, ITA, BRA, SPA, GER, FRA, ENG, ARG
Second tier European teams:
HOL, POR, SVK, DEN, SLO, SWI, SER, GRE
Conmebol and African teams:
PAR, CHI, URU, CIV, NIG, ALG, GHA, CAM
Concacaf, Asian and Oceania teams:
MEX, USA, HON, AUS, JAP, KOR, PRK, NZL
The draw will be made so as there is no more than 2 European teams in a given group and there is no more than 1 African or Conmebol team per group. So the African teams will not fall in South Africa's group, and the South American teams will not fall in Argentina's or Brazil's.
Politicking is being made by Concacaf, to exchange post with second tier Conmebol teams (and thus facing Asians and NZL, instead of African teams).
This is an example of a fake draw, made by a Mexican radio station: