It's nice to celebrate Valentines day with a single Rose or a Bouquet. The secret to making nice flowers is using nice yarn. Cheap, acrylic yarns look kitschy in a "memories of granny's bathroom decor from the 1970s" kind of way. Using a decent wool, something with some surface texture and depth of colour (single plies look nioce), goes a looong way! Plus, if you use a feltable wool and aren't keen on the finished texture you can always salvage the project by felting it. Lamb's Pride Worsted is a good option, it has a bit of fuzz to it, or try Malabrigo Merino Worsted in a semi-solid for a very knitterly aesthetic.
Knit some Mini Hearts or some Super-mini Hearts or are great valentines decorations: string them together in a garland or mobile.
You can also Crochet Mini-Amigurumi Hearts or Medium Hearts