Mental projection allows one to enter into the 'mind space' of any symbol and also to alter things associated with the sigil. For this exercise you will need to find a magically complete symbol set, by which I mean any symbol set that is capable of expressing any concept within reality to a greater or lesser degree of precision.
Elemental symbols are good and are fairly traditional but as long as completeness is satisfied (this is for long-term reasons, not a temporary operations; a magically complete symbol set gives you a complete input/output instruction set and this is invaluable) anything you want to use that for you objectively expresses the concept will work.
For this exercise first you will need to mentally project into the mental domain of the sigil. Explore around a bit, see what is happening and then acquire the signature of target from the domain of the sigil. Once this is done, begin projecting deeper into the target, noting anything you sense along the way until you reach core.
Everything you have sensed expresses the relationship of the target to the particular concept represented by the sigil. This can be modified to alter the target in varying ways. For example, if you wished to use this to increase someone’s strength you may use a fire sigil. Along the way you may gain an image of the target outlined in fire but with their heart dark, and you may associate heart with the coordination of energy. You might glean from this that their strength is suboptimal due to the fact they don't have the necessary mental patterns to coordinate their energy and from this insight create a series of triangulating links from the fire-realm of the sigil in pure form, the fire outlining them and their heart until it is burning brightly and the fire is flowing freely throughout every part of their being.