The equivalent of Levels in Lightroom is Exposure for the white point (well, it does a bit more than that), Blacks for the black point, and various sliders affect those the middle gamma slider does.
I was used to working with ACR 3 before I got Lightroom and ACR 4 in Photoshop CS3, so the Develop module in Lightroom is familiar. There was a good ACR tutorial posted in these forums - from which I've developed my own version.
I find the best workflow with Lightroom is to turn auto tone off. I have a preset that sets Exposure, Recovery, Fill Light and Blacks to 0, Brightness to +50 and Contrast to +25, Vibrance and Saturation to 0, Curves to the default (all six sliders in their default location) and Medium Contrast, and all the HSL stuff to 0. That's a great starting point for adjusting things yourself.
The first thing that I do is adjust White Balance - usually by setting White Balance with the eye dropper in a WhiBal shot, then synchronising that to the other shots in the same lighting.
I find the best workflow from there is to turn both the clipping warnings on (the boxes you can select in the top right and top left corners of the histogram), and set Exposure first, looking at the histogram and the clipping as well as the image itself. Usually you're aiming to get the right hand end of the histogram at the right of the available space without too much clipping showing. If necessary, adjust Recovery to bring back the clipping. Your ideal is no clipping, but there are some areas, such as light bulbs and specular highlights that you probably have to let blow out.
Hopefully your Exposure setting, unless you're deliberately doing something a bit radical, is no higher than about 0.7 - if it is, you underexposed the shot quite significantly. If you're "exposing to the right", chances are that you'll have many of your Exposure settings a little to the negative side. In a RAW workflow, don't get too upset about a bit of blinking in camera, as you can almost certainly get it back in the RAW converter and, indeed, it may be a sign of good exposure to the right. However, too much blow out and information has been lost. Be particularly careful in cameras that don't offer separate R, G and B histograms (like my 20D) - it's possible to blow one or two channels out more than you realise.
Once that is done, adjust Blacks to maximise the tonal range - again, watch the histogram and the clipping. You're trying to get the left of the histogram to touch the left without too much clipping - a tiny amount in the deepest shadows is fine, but too much and you'll lose shadow detail.
A bit of Fill Light can lift your shadows - though it's best not to go too mad, especially as this can introduce noise.
It's a bit of an iterative process - once you've adjusted all those settings once, you may want to tweak them a bit; I suggest you tweak in the same order, especially if you're not sure what tweaks are needed. Don't forget that you can take Snapshots and you have the History as well.
If you hover over the sliders with your mouse, you can use your up and down cursor keys to adjust the setting - if you hold down Alt (or the equivalent on the Mac), adjustment is slower, which is particularly useful for Blacks.
Once you've done that, you can adjust Brightness, Contrast and the Curve settings to suit - there's an excellent video on the Adobe site about the Curve settings, which I suggest you watch. Often a little bit of Curve tweaking can produce a much better image - but extreme adjustment is often not needed.
I may then tweak Vibrance a little, though I'm no fan of Velvia like photos. I find no reason to touch Saturation now that we have Vibrance.
From there, you may want to do a little in the HSB settings if the colour is a bit off - or adjust the black and white settings if you've decided on a black and white image (Virtual Copies can be useful here; if you've got a good colour image as a starting point, you can create a Virtual Copy and experiment with with the sliders that dictate the black and white conversion).
Vinni is quite right - you can do everything with the Curves dialog in Photoshop that you can do with Levels, and a lot more besides. Curves in Lightroom are a bit different, as they don't have white point and black point sliders - nor do they need them, as you've already set those with Exposure and Blacks.
There's absolutely no need to drop to Photoshop for Levels adjustment; Lightroom provides all that you need for the majority of your images. Indeed, Levels on the entire image really shouldn't be necessary in a good RAW workflow; you're far better off making the changes you could make using Levels at the RAW conversion stage, for example using the workflow I've described. Making such changes on a 'cooked' image is less satisfactory (and completely unnecessary in Lightroom or with ACR 4, which can work on JPEGs and TIFFs, though it's better to start with RAW).
I don't like the auto tone adjust in ACR / Lightroom - sometimes it's interesting to see what you think, but I find I get better results if you turn it off and DIY. You soon get quite proficient in what you're doing.
As always, a calibrated monitor is important if you're going to make good judgments about colour, contrast and the like.
David
