Advanced techniques for Roux
There are a couple of techniques which come to mind for improving you blockbuilding and influencing later steps and such.
Influencing the second block
Influencing the second block during the first block may not sound very specific or important, but it's crucial to get your times as low as possible. Here are a few cases, experiment with them, then make some of your own:
Making the second block not too inefficient
The second block in Roux is usually where we all get frustrated with high movecount, and feel there's not much to do about it- some cases for the second block are really annoying. You can try to apply Multi-slotting to reduce cases. There also are many cases where it may look like it'll take many moves, but it won't. Here are some cases which may not be immediately apparent in solving.
KCLL is what coms to mind here. It is basically influencing edge orientation while solving the U corners. Notice it's not necessarily solving EO, but influencing it. Sometimes solving EO may be more trouble than just influencing, say, a 4 flip then simply doing M'UM'. This is why it helps to know multiple algs for each case.
You can change EO by just inserting a slice move before an alg. A very obvious case is if you got a Sune case with UF and UR flipped. If you insert the M' before it, to make r U R' U R U2 r', you flip the edges, with literally no extra moves. This comes in handy as some EO cases take many moves to execute, like 2 flips or the 6-flip.
OLLCP can be applied here too. And if DF and DB are oriented you can solve Eo easily during CMLL.
You were always told to orient your centres first before doing EO. But sometimes, it's useful NOT to, or to make centres free. You see, an edge that is not an L/R edge is oriented if it has the same orientation as the centres. Whilst the L/R edges will be oriented if you have your U/D colour on top/bottom. So this leads to some fun.