Inscription: 351 - 450
351 - 355: 95 x Ink of Sea. Suggest you put on a pair of headphones and listen to your favourite music. This is gonna take a while...
The next batch would be scrolls. And lots of it. Keep in mind though that most of these scrolls dont sell very well on most servers. So if you can use it then you might as well do so while you are leveling. Or you could send some to your alts.
356 - 360: 5 of Scroll of Spirit VII.
361 - 365: 5 of Scroll of Intellect VII.
366 - 370: 5 of Scroll of Strength VII.
371 - 375: 5 of Scroll of Agility VII.
376 - 380: Use up all the Icy Pigment you have and start making Snowfall Ink. Keep the extra Snowfall Ink for Northrend Inscription Research. You will need to research to learn most "Northrend" glyphs.
Keep in mind you are going to need a ton on Northrend herbs from here on. So lookout for cheap priced ones on the Auction House.
381 - 385: Choose any glyph that looks orange to you and make 7 of them till you reach 385.
386 - 386: At 385 you would be able to conduct "Northrend Inscription Research". If you are not in a hurry I would suggest you keep doing them on a daily basis, (has a 20hr cooldown) for a few days/weeks. Or you could just do it once and proceed further.
387 - 400: Choose any one of the discovered Major Glpyhs and make around 25 of those till 400.
Another batch of scrolls. But these might actually sell well depending from server to server.
401 - 405: 5 of Scroll of Stamina VIII.
406 - 410: 5 of Scroll of Spirit VIII.
411 - 415: 5 of Scroll of Intellect VIII.
416 - 420: 5 of Scroll of Strength VIII.
421 - 430: 13 of Scroll of Agility VIII.
431 - 450: The best strategy here is to stop leveling Inscription at about skill 430, and simply conduct regular Northrend Inscription Research. Or if you are impatient to hit 450 you could continue to make scrolls or some of the other epic items available to you now, like Epic Off-hand equipped tomes, and the infamous Darkmoon Card of the North.
Tip: If you have the money or enough northrend herbs lying in your bank, convert them into Snowfall Ink and Ink of the Sea and make a lot of Darkmoon Card of the North. This has a chance of giving a random card of either Noble, Undeath, Chaos or Prisms. You can combine these cards to make a deck of each type and sell them for insane amount of gold or sell them individually too.
Also keep on the lookout for Book of Glyph Mastery. These are random drops from all Northrend Instances that teach you a random Glyph that cannot be learnt otherwise by normal Inscription Research.
That's all for now. Hope you liked this guide and could put it to use wherever possible. Do come back for more for more advanced tips and strategies on inscription and how to make good use of the profession to make lots of gold in your WoW career.