Unfortunately there is no universal method for identifying fungi. The amount and type of characters needed depends highly on the group of fungi you are studying. If you are working with soil fungi, it´s probably mostly just hyphal and other asexual characters, and possibly (e.g. with zygomycetes) some sexual characters. I´m not expert on soil fungi, but I suggest you try to find some basic information of soil fungi (start from very basics, like http://urbanext.illinois.edu/soil/SoilBiology/fungi.htm ), and then try to find some litterature on the groups or genera of fungi that are likely in your area.
Quick googling with "soil fungi" you get what seems to be accurate and probably informative for you, e. g. http://www.sciencemag.org/content/346/6213/1256688.abstract
...but often the only way to identify fungi with certainty is to sequence DNA.
You may go with the Coconut Agar media for the confirmation of aflatoxin producing fungus species as the cultured plate give yellow florescence under UV radiation.
You can also identify by using biochemical testing methods.
Soil fungi and isolates from roots are the most difficult situation. Especially as the fungi growing on your plate may be different from those you saw on your root samples. You may need to visit your university's library and search for titles like "catalogue of basidiomycetes/ascomycetes/zygomycetes from XY".
A nice online resource is http://www.mycology.net/ . They even have some online identification keys.
You can also check http://mycology.adelaide.edu.au/ . This is about Australian fungi, but maybe the information is helpful for identifying higher-order fungal groups.
Are you familiar with polymerase chain reaction and associated methods, especially cloning and sequencing of amplified DNA? This can be more precise, save you a lot of time and give more stable results. I can list you some references, if you like.
This paper may help with visual identification: https://www.researchgate.net/publication/275335972_A_review_of_fungal_contamination_in_pharmaceutical_products_and_phenotypic_identification_of_contaminants_by_conventional_methods
Article A review of fungal contamination in pharmaceutical products ...