Asbestos business is a serious one: one is playing with human lives!...Downplaying the difficulty and expertise is foolish.
You need a good prep: clean glass slide, clean cover glass, immersion oil, good dispersion of all particles and clumps.
You need a good light microscope: good adjustable light source (filament alignment and variable intensity), double diaphragm, Köhler illumination. Binocular viewing is best for avoiding eye strain.
You need a good 40x objective, a 10x ocular eyepiece. You can do without a phase constrast device, but then your expertise should be at a very high level.
You need some expertise to recognize each of the different asbestos fibres: crocidolite, amosite, chrysotile, which look quite different. Morbidity and regulations are widely different for the various asbestos-types.
You need even more expertise to distinguish asbestos fibers from other fibrous silicates (fibrous talc, wollastonite,...which are also found in indoor households), from asbestos-looking Ca-sulfates (bassanite, gypsum, which are widely released in the outdoors by community heating with fuels), from chrysotile-like organic fibres (cellulose=kleenex), etc., etc. This is why your microscope should better be equipped with polarizers.
Sorry to say that: if you are not a well-trained expert, either you will never find asbestos (chances are that you are optimistic, or that you fear the expenses), or you will find it everywhere (if you are pessimistic or paranoiac).
J.J.