I usually extract lipids from tissue using the Folch method and separate/quantify TGs using HPTLC+densitometer. But if using a colorimetric method, you would need to lysate the tissue using an appropriate buffer, centrifuge and follow the kit instructions.
I usually the Bligh, E.G., & Dyer, W.J. (1959) extration total lipids and purification. Canadian Journal of Biochemestry & Physiology, 37 (8):911-917. Narcisa Bandarra
The lipids have solvente apolar afinnity , these can be used in lipids extration, allowing their quantification by gravimetry.