Index convention for tensors

[Schuller 2013]
In order to use Einstein summation convention it is needed another convention to put index upstairs or downstairs in vectors, 1-forms, coefficient of vectors, of 1-forms, and so on.
Given a vector space $V$ , the convention is:

The basis vector of $V$ carry downstairs indices: ${e_{i}}$ .
The basis vector of $V^{*}$ (the dual vector space) carry upstairs indices: ${e^{i}}$ .
All other placements are enforced by Einstein's summation convention. For example, coefficients of a 1-form must carry lower indices:

σ = σ_{i} e^{i}