Any tips for a first time Dual Rectifier user?

I got my dual recto too lately (2ch tho) and I noticed that with Les Paul type guitar with EMG's (LTD EC1000) you need the tubescreamer type pedal to tame the low end (drive at minimum, tone tot taste to cut the excess fizz and volume either halfway or max), otherwise it is really woofy and wild.

For rhythm tone start with modern red channel, master volume as loud as you can while still being in the same room (Mine usually stays around 9:00), preamp gain between 12:00 and 3:00 to taste, tone controls at 12:00 and then adjust to taste. At least with my guitar I need to keep the mids pretty low, between 8:00-10:00, because it sounds really muddy otherwise.
 
Honestly, in my experience, the Dual Rectifier is NOT and easy amplifier to play. You really have to have your shit together in order to control it and get what you want out of it. Switching from my Dual Rectifier to my 6505+ is like switching from a F1 car to a go cart. When I play the 6505+ I almost feel like I'm cheating because everything seems to come along so much easier.
Yes, I noticed that this amp is not very forgiving towards sloppy players ;-). The gain has to be very very low (or it turns into a muddy mess) and you have to play tight... very tight. Not one of my strengths ;-).
My advice would be to get a drum track, and write a riff, double or quad track the Dual Rectifier and adjust the rest of the mix to match and then see how you feel about it.

I've never been able to force the Rectifier to sound like anything other than how it sounds naturally. It works really well in a mix, but I find the mix has to be adjusted to suit it and not the other way around. I've always hated how my Rectifier sounds solo'd, but in a full mix? I adore it.
Good advise, this might explain why a song that I retracked with the Recto (had been done with the Bugera before) sounded like the total shit but a new song from scratch recorded and mixed around a Recto-played riff, sounded quite OK.
 
For rhythm tone start with modern red channel, master volume as loud as you can while still being in the same room (Mine usually stays around 9:00), preamp gain between 12:00 and 3:00 to taste, tone controls at 12:00 and then adjust to taste. At least with my guitar I need to keep the mids pretty low, between 8:00-10:00, because it sounds really muddy otherwise.
Those settings are WITH the Lube Slimer pedal, right (at least they sound to me as if they are)?
 
I've been playing various Rectos since 2003, and if there's one thing I've noticed its that when you haven't played one for awhile they feel sluggish and your timing feels really off.

Personally, I feel that you can control more of the Rectos tonality with your pick than you can with the EQ. It's a trade off... that momentary lag gives you depth of distortion, however you have to develop the ability to control it via your pick attack. With time (and suitable pickups), you can thrash that amp without an overdrive boosting it.

Over the last 8 years I've only ever used a boost for a couple of months... usually when using passive pickups. With an EMG 81... there's no need (IMO).
 
I've always hated how my Rectifier sounds solo'd, but in a full mix? I adore it.

You're bang on the money there! I tried several Rectos in shops and at friends' places without really understanding the hype. I then borrowed a Triple Recto from a good friend for a short tour and played a few gigs with it... I was blown away! I'm so used to the amp now that it sounds great to me solo'd, but it's in the context of a mix where a Recto shines like no other amp I've ever played.

I've got a Triple Recto, which will sound a bit different from a Dual. So far I've mostly used it live. I prefer channel 3 over channel 2 for high gain, although I have a friend who has the complete opposite opinion. My gain knob is rarely higher than 12-1 o'clock, and that is without using a TS in front. I also run the bass control very low, I can't believe that some of you guys are running it at 12 o'clock.

You need to pick really hard and precise to get the amp to shine, I had to lower my string gauges because I couldn't pick hard enough consistently to get enough attack with the .070 B string I had on my Schecter. But I couldn't be happier with how it sounds now, and I'm recording guitars for a couple of new songs soon :D