Agonizing? It’s an adventure! Lol. I’ve done this on 12+ characters, and I think I’ve been killed by enemies like twice when I wasn’t jumping into a battle. It’s not too hard. Tips:

Which campaign?

Obviously if your server has a non-populated campaign where your faction dominates, this would be best because the keeps will be open for you. If not, I like just using the busiest campaign because the keeps will flip as your team pushes and there’s usually enough activity to get your shards in a couple of trips.

Routes

I divide the map into three loops. (I use an iOS / Android app on my iPad called The ESO App, which has maps of everything and I find to be indispensable and utterly worth 99 cents).

One loop extends from EPs north base all the way south to the slaughter fish river. Eleven overland, seven delves. Your only true “danger zone” is Cracked Wood Cave, which often has PVPers looking for a boss. Be cautious here. The second loop extends from ADs east base up to the northwest all the way to Bruma. Ten overland, six delves. The delves in this loop are pretty busy...watch out and use invisibility pots. Loop three takes you from DCs bases to the east, seven overland and six delves. Pretty low traffic.

Get books

If you’re working your mages guild, look up book locations in advance. There are many collections that can only be completed in Cyrodiil, and you might as well grab these books if you’re working to unlock comet / passives.

Speed tips

You’ll want retreating maneuvers...no brainer. I also temporarily allot my champion points to unlock War Mount (green 120 CP passive) so that I get endless sprint while doing this. For me it’s worth the gold to respec CPs a couple of times. If *** this, you could also pile into the crit resist red passive if you’re worried about human enemies.

If you’re open to spending a little for gear for this mission, Shadow Dancer is a magic set that allows you to sneak at fulls speed...very helpful. (Night Silence is the equivalent for stamina characters). Shadow Dancer is pretty cheap in guild stores.

Invisibility pots

Blessed thistle, blue enteloma, namira’s rot. If you’ve fully invested in the alchemy passives, you get 16 seconds invisibility and 45 seconds speed. Note - try not to use these while your retreating maneuver speed is up, sometimes it glitches and cancels speed all together.

These pots will help you disappear if you encounter an aggressive human enemy. They will also let you get most of the way through a delve to a shard just walking past NPCs. You CAN NOT take damage or cast abilities while invisible, so learn to proc them at the right time to avoid wasting them. If in doubt, dodge roll then proc. The roll angels incoming hits.

The dreaded gate shards

The six shards behind the scroll gates will be the hardest. Obviously you have to wait until your faction opens those gates to get the 2/2 shards at enemy bases. Once the gates are open, assuming there’s not a human fight right at the gate, it’s not so hard. You want to sneak through the gate, then mostly you’re home free.

There are two techniques for sneaking through the gate. One is to get as close as you can without the npcs spotting you, then proc an invisible pot and walk through. The down side is that they have a really long reaching detect radius, and it can be hard to make the whole distance since you can’t run while under the pot.

The second technique is my favorite because it’s a bit crazy. I wait until I’m full stamina, then I mount like mad through the gate. When my mount stam is down to 33% I dismount quickly (beforemthey knock me off), then dodge roll 2-3 times then proc my invisibility pots and calmly walk away. Once through you aren’t really at risk...you can get to the shards without meeting any NPCs.

Hope that helps, good luck!