First thing is to read, read, read the posts in this forum. There's tons of information from some very experienced engravers on here. I have learn't loads and picked up lots of tips.
I have only been into this process for a couple of months myself but I am thoroughly enjoying it. It still amazes me how intricately you can work on these machines.
I have a 40W 4060 size machine and so far so good.
Firstly, your cooling system is very important. It's a good idea to turn it on 5 minutes before you use your machine and leave it running for maybe 30 minutes after. This will help maximise the life of your laser tube.
Secondly, your extraction fan is fairly important. The laser works by vaporising the material being engraved and as a result smoke and fumes are produced. Without this the laser cabinet soon fills with smoke so you'll not be able to see what's going on in there. It'll also mean you will need to clean your mirrors more frequently.
However, I think you can have the fan unit some distance away, connected with the ducting to your machine and it will still pull the fumes and smoke out.
Engraving wood produces a lot of smoke and it has to go somewhere.
Finally, be prepared to practice on lots of samples. Try different speed and power combinations until you get the right result. Make sure you keep notes as you'll soon forget which setting where for which material.
When engraving images, put some effort into producing the image or your resulting engraving would suffer. A good photo editing suite will pay dividends. I would also consider some software called PhotGrav. This will save you a lot of time and will edit and convert your images to the right format for your machine.
Here's what I do - Select my image and open it in my photo editor. Adjust the resolution (read posts on this forum for more info) and the final size of the image. Do my cropping etc and save in an uncompressed file type (I use .tif)
I then open my new image in Photograv, select the material I want to engrave on to and process the image. This will give me a realistic visualisation of what the final engraving will look. I then save it as a .bmp file.
Now I have the finished file I can import it into my laser driver software and send it to the laser.
Hope this helps at least a little,