– A recommendation from a client is usually not recommended unless it is a very impressive client (big name firm). However, recommendations from clients can serve as a way out for people who have only worked in family firms and don’t have other potential recommenders to choose from.
– If possible, it is better to select recommendations that provide different angles on the candidate.
If two recommendations describe pretty much the same type of activity (e.g. rec. 1 – programmer in company A, rec. 2 – programmer in company B), one of these recommendations should probably be replaced.
– Recommenders who are alumni of the same school that the recommendation is submitted to are more effective than non-alumni recommenders (not critical, but helpful).
– Recommendations from very big shots (e.g. government ministers, famous people) are great if the context is of mutual activity (preferably direct/indirect supervisor) and the content reflects acquaintance and excitement. If not, they don't necessarily help and may even hurt.
– Pay special attention to the "recommendations instructions" section that each school provides (instructions to the candidate – which recommenders to choose etc., and instructions to the recommender). Their specific requirements must be met.