Shall be fitting mine tomorrow.
I have never in my life managed to fit anything straight.
How do I stand the best chance of getting both races in line with each other and lined up with the centre of the bike?
I fit a superstar one with a bit of grease and a rubber mallet.
It was way easier than I expected.
Hopefully that's not jinxing me, as I have another to fit soon.
A headset press pushes them in squint (because there are squint). Press + mallet whacks to de-squint or just don't use the press.
I've fitted a couple, definitely better with a mallet and a block of wood, don't bother with the headset press. I put some masking tape on the top tube and head tube so I could mark the centre points to line up with, bit of string around the seatpost works well for marking the centre. I also found using the headtube badge useful as a reference (assuming it's central).
Put the cups in the freezer overnight
Make sure you put it in the right way around - a briefly employed mechanic at my LBS put the top headset cup in backwards on one of my frames, which I spotted immediately. So he took it back into the workshop and after short while brought it back out, having removed it and put it back in backwards again! Third time lucky...
Bit of measuring/marking with a straight thing- random bit of wood is good enough. Then precision fit it with a rubber mallet. (I use a mallet for all headsets these days, it just works, but specifically with anglesets I did find that my headset tool that I had liked to rotate it in the frame which was super annoying)
And don't fret too much, it's not that hard.
Yep, string/cotton on seat tube to mark centre of headtube and put cups in freezer over night.
Don't use press as it will twist so piece of wood and hammer.
If its the Works Components one, they have a groove top and bottom. I use a piece of long key steel and rest it in the groove, eyeball that its straight along the top tube.
Headset presses dont work, I use a small offcut of 10mm OSB board and a 16oz plastic faced hammer. I even put normal headsets in the same way.
That went well . Thank you Mr Giant for your excellent stickers.

Lined my Works one up and tapped it in with a plank of wood and a mallet.
Now I love having a hardtail with a 63.5* head angle.
Never had a problem with using a press and fitted an Angleset twice with it.
I lay a piece of string from the seatpost over the headset markers to make sure it was all straight, and press one cup in at a time.
Easy