You get free boots at 10 min. but you cannot buy boots before then. These boots give additional MS. For each takedown you acquire the boots 30s sooner.
Guardian synergizes well with Taric's [W] when looking to block big incoming damage and the extra burst of Movement Speed allows your to position yourself to land [E].
WhyFont of Life
Taric loves to build Increased Healing/Shielding items so proccing Font of Life with [E] will result is a lot of healing for your teammates when you they hit the enemy champions.
Conditioing on Taric makes you a big front-line tank in the mid-game and your natural synergy with Armor will make you and your linked [W] ally difficult to take down in skirmishes/teamfights.
Revitalize synergizes well with both [Q] healing, [W] shielding strength, and Locket shielding making your teamfight damage mitigation incredibly strong.
Biscuit's massive mid-fight health regen when you are below 50% will allows you to absorb a ton of poke and front-line damage thanks to your natural high resists.
Magical Footwear is an all-around good rune choice on nearly every champion. It act effectively as a free kill's worth of gold at 10min allowing you to hit your combat stat item pokwer spikes even sooner.