Just apply a tiny amount of highlighter to your cupid’s bow (the M shaped area on your upper lip). Doing so adds light to this area, giving the illusion of larger lips.
Any pencil, powder, liquid or cream highlighter will do. However one of my favourites is the much-loved Jaclyn Hill Shimmering Skin Perfector Pressed in Champagne Pop 13ml (£32.00 cultbeauty.co.uk / $38.00 Sephora). It is a apricot-gold highlighter that is easily blendable, highly pigmented and flattering af on all skin tones.