Got an old smoker. First timer, how do I restore this thing?

Welcome aboard.

Without being right there I suspect you'll just need to follow the propane line to the burner which is likely in the firebox as an alternate fuel source.  I can't tell what the vee shaped part at the right of the firebox is. 

A good brushing followed by soaking in hot soapy water and another brisk brushing will probably get the cooking grates ready for use and a good brushing to get any rust and scale off the interior of the smoking chamber followed by a coat of veggie oil is in order.

Wood ashes are corrosive so I'd give the firebox a good scraping and brushing and consider a couple of coats of high temp paint in the interior.  You may want to fabricate a simple ash pan to sit in the bottom of the firebox and keep ashes off the bottom since I also suspect the steel is pretty thin.  Just a simple sheet of thin sheet steel laying against the curve of the floor of the firebox will extend it's life.

Is that a cooking grate in the the firebox above a wood grate?  At any rate it looks like it will need a bit of repair.  If it's a cooking grate you might want to take it out when you aren't using it to extend it's life.

If the burner is rotted you may be able to find a suitable replacement at a home center or good hardware store.  Given the way things are merchandised you may have to wait for grilling season in your neck of the woods to find grill parts in stock.  Get a hose and regulator of appropriate length too.  That rig looks like it had an unintended fire I wouldn't trust either.

Where are you at?

Lance

Good wire brush (one mounted on an angle grinder if you got one works great), knock off all the rust, paint the outside only with some Rustoleum High Heat paint (available at Lowes, etc.), good coating of veggie oil on all inside parts of the cook chamber, build or buy a charcoal basket for the firebox, heta it up and smoke some goodness.  After painting and after the first fire, you can rub the firebox down with some veggie oil as well, this will help protect it a bit longer than just the paint.  As far as the propane, looks like a mod, you can always work on this after you get the smoker back to working order.

JMD, evening....  Ski Freak did a mod to his smoker.... Independently adjustable FB air inlets.... he came up with an ingenious idea pictured here...  the lower air feeds the fire for more heat..... the upper air allows the heat  in the fire box to move through to the cook chamber....  He says it works awesome and he has great cooking control....   

Looking at that smoker, it sure looks like it will be a dandy.....  looks like the doors will need a little tweaking and some type of seals to make her air tight....  won't be much work but worth it....   Good luck.... lookin' forward to the first smoke....  Dave

Looks a lot like a Braunfel Black Diamond Smoker....one heck of a fine smoker and with a couple tweaks like Mr Omak mentioned, superb. Brush her down, burn it out, and hit it with a good coat of  high temp and you're set. Lance mentioned above about adding a liner in your fire box, not a bad idea, a lot of folks neglected these and they will weaken on the bottom of the fire box without proper care. Good luck!!

I bought an old New Braunfels Black Diamond a few months back.  Took it down to the bare metal and restored the entire smoker.  I added the following mods:  1.  Fully welded charcoal basket, baffle, extended the chimney to the grate level.  It cooks like a champ.