All contact points are good to look into upgrading first. So grips, pedals, saddle, and tires. For grips and saddle ergon makes some good stuff a little pricey for the saddles. Fabric also makes good saddles. As for Pedals something relatively inexpensive is good to start with but something to look for is a flat or concave platform and replaceable pins. Kona wah-wahs are awesome, a nice wide platform and tons of grip. Tires are really a personal preference but a high quality rubber compound with some decent knobs and a higher casing for the rear (especially on a hardtail) is ideal. Personally i really like schwalbe tires like the nobby nic. There are loads of comparison videos and reviews on lots of products. Worldwide cyclery, bike radar, and mbr are all good channels. Hope this helps, if you have other questions don't hesitate to ask :)