I use long sword/great sword and occasionally dual blades. My main strategy was to just come in from the side and hit one of its legs or move a little further back and work the tail a bit. Once it starts falling over I work on getting its tail.
If using LS og GS, maybe try going after the ass. Some of it will land on the tail, some of it on the legs. It requires more time in some situations to walk around and get there (if he's facing you), but it has the advantage of placing you further away from the face.
Just stating the obvious here, but if getting hit too much, make sure to wait for him to commit to a move, and only then (if you have room and time), go in, land a cple of hits, roll away.
It can be a bit of a war of attrition in the early goings. When he eventually gets hungry, you get ginormous windows to f his s up, ganster-like. As you get more comfortable with his moveset, you'll be able to read him instinctively and just start mauling him right away.
Any tips for Diablos? I fought him online with a few GAF folk last night for the first time. He seems somewhat difficult to get in and hit. Every time I got close, he either swatted me away or headbutt me into submission.
Bring sonic bombs (screamers+gunpowder, screamers from great jaggis, I think wroggis, baggis and maybe qurus as well, it's a "bag" item, gunpowder from fireherb+nitroshroom). Use sonic bomb when he burrows, throw it as the tail is disappearing underground. Be wary that it only works when he's not raging (look for black smoke coming from his mouth to see if it rages). There are 2 indentations in the wall in 8 into which you can climb. If you stand there and he charges, his horns will get stuck in the wall (if he has horns left). The pillar of the stone arc works the same in area 10. Roll away or superman-dive at the last possible instant. Be patient, early on it'll feel like you're barely making any damage. He will get tired and give you opening.