Apart from what Lasse said:
Doing Nightfall and Weekly Heroic Strike is a most efficient way to get those. Weekly on max difficulty is a guaranteed 9 coins at once. Nightrall is a bit more random, but has a chance to give coins, exotics and old ascendant materials (and a weekly exp bonus!).
See more on wiki.
Ascendant materials (old ones):
There are plenty of those in Vault of Glass raid (and some good loot too). If you can find a team that knows what to do, then it doesn't take much time to run it. It has 4 loot drops and 3 chests (4 if you can beat Templar without teleporting). So you can end up with plenty of materials. See more on wiki. If you don't have a group, then try Destiny LFG, there was an official Bungie blog post about this site, it helped lots of people to find a team.
Also, if you're short on ascendants but have some spare legendaries or exotics, then don't forget to level them up completely (no need to purchase perks) - legendary guns have a chance to give up to 6 Energy on dismantle (up to 3 if vanilla), and any such exotics will give 2 shards (only 1 if vanilla).
Vanguard marks are best farmed from strike playlist. The best one right now is Roc - it gives rep, marks and guaranteed engram. If you do those, not only you get your 100 weekly marks quick, but you also get lots of engrams (basically you increase your change of getting legendary gear through sheer number of engrams you get, and cryptarch packages when it levels up). If you don't have The Dark Below, then Tiger playlist is your best bet, it has less rewards though, but same amount of marks.