I've been playing Earth Spirit a lot since his initial release, and I've been experimenting with certain builds. I find this one to work for me the most:
Get Rolling Boulder at level 1. OMFG this is such a good skill early game. When you go get the rune with your lane partner, land it on the enemy, then bodyblock them. I had so many first bloods like this. Otherwise, it can be used to escape those early ganks.
Itemwise, I would almost always get bottle first, even in sidelanes. Once I get this item, I usually like to go for kills in my lane, or rotate to other lanes (not if I'm mid). This way, you can get levels faster and get your supposed MUST HAVE items. After Bottle, I like to get brown boots and stick with it. Although Arcane Boots and Power Treads can be better, Brown boots can be enough for a hero like Earth Spirit.
The first core item I personally like to build is Veil of Discord. Seriously, the extra 25% should never be overlooked when combined with Magnetize. Using it on a lone enemy also gives some significant damage boost. After that, I like to blink a lot. It gives good positioning and adds an already ridiculous escape to Rolling Boulder. You can go blink before veil but I prefer to get good magic damage early on, as Earth Spirit's damage tends to fall of late game.
Situational items I like to go for are Eul's Scepter of Divinity and Force Staff. Eul's can do the usual invulnerability, but also an awesome setup for your other skills (if timed correctly).
For your skill build, you ALWAYS ALWAYS ALWAYS do this: 2-1-3-3-3-4-3-1-1-1-4-2-2-2-stats-4-stats
Maxing Geomagnetic Grip is kind of obvious. Its damage is the highest among your first three abilities, and its pretty easy to land as well. Take advantage of that. You would then want to max Boulder Smash second. Its' a really really powerful stun if properly optimized, and the 10 second cooldown by level 10 makes it spammable. Wait... a 2 second+ AOE stun with a 10 second cooldown at level 10? SHIIIIETTT. Seriously, train it well enough and it can be just as good as Ravage. Think about it.
As for the combos which I'm sure your struggling on, when initiating on a lone enemy I usually prefer to do this:
Use Rolling Boulder in the direction of the enemy. During the 0.6 seconds form time, place a Stone Remnant down and immediately pull it using Geomagnetic Grip. Upon arriving at the enemy, he/she/it should now be slowed AND silenced. Use Magnetize. After the silence is over, immediately place a Stone Remnant down and use Boulder Smash on it, stunning the enemy. This will mean that the enemy cannot do anything for 6 full seconds other than move and use items. With good practice, this can net you some good delicious solo XP. The Roll-Pull combo is also good in case you're facing an enemy like Anti Mage, Faceless Void or Mirana. If you simply use Rolling Boulder THEN Magnetize, then they would have a small opportunity of escape. Using Urn of Shadows and Veil of Discord gets the job done faster.
Now, let's talk about Aghanim's Scepter. If you can use this item correctly, FOR THE LOVE OF RNGESUS GET IT. This is how you can use it to show of your brilliant micro skills:
Turn your ally to stone and kick them away, saving them and giving them a 2000+ unit displacement from the enemy. When starting teamfights, you can use it to transform the enemy to stone and kick them towards your team, something like Flaming Lasso on steroids. Turn an enemy to stone and roll over them for an easy escape (TIP: you can cast Enchant Remnant while rolling) Turn an enemy to stone and stun/slow/silence ANOTHER enemy. Use it as a temporary disruption on enemies until reinforcement arrives.
Late game items that are good on Earth Spirit are Shiva's Guard, Scythe of Vyse and also Ethereal Blade. These items grant Earth Spirit more disables, and can help him boost into the late game. Ethereal Blade gets an honorable mention, as combining it with your other skills can guarantee a high boost in your magical damage.
As a final reminder, NEVER EVER pick Earth Spirit against a Bristleback, Medusa, Anti Mage, Huskar, Chaos Knight, or any other hero like them. They have high resistance to damage, especially Earth Spirit's magical damage, which does not scale well against them.
That's about it.