Start with really low concentrations - 0.025% or even retinol in ester form (retinyl palmitate, retinyl acetate), they're gentler than pure retinol. The main rule: apply it 1-2 times a week, no more often, and definitely on dry skin with a 20-minute gap after cleansing to reduce irritation.
Plus a regular moisturizer on top - buffering reduces burning and flaking. If your skin is really acting up, try alternating days: retinol on Monday, then a week without it. I'd also recommend not mixing retinol with other active ingredients at first - you add vitamin C, acids, and all that later, once your skin gets used to it.