Lumen, I'll try to help - but I'm not sure what stage you're at! I just solved as many clues as possible. Some of the others proved more tricky, until I realised what was going on - or what was being taken out! One example...
20 Relet low-down ruin for housing. I could see Info, low-down, hidden in 'ruin for'. The 'relet' meant nothing until I saw that the 'sequence of letters' would be 'van', to form Relevant so it was actually 'Relevant low-down = info'. I think other examples have been given earlier. I spotted enough of these to know what the general theme was.
The preamble says that '...12 clues a single letter must be removed before solving'. I found those easier to spot, and the ones nearer the end of the clues indicated the second part of a phrase/thing. The examples mentioned earlier all fit the description of the first part of the phrase/object.
Is this any use?