I would do a good PM on the machine. Change rear diff/tranny fluid, engine oil/filter and front diff fluid. Grease up all the zerks. Just so you know where you're starting from as far as maintenance is concerned. I would also invest I a Battery Tender to keep the battery at peak performance.
Pick up or download a service manual too. Worth their weight in gold for the do-it-yourself type of person
This is "spot-on" advise!!
But to expound on this a little.... Personally when I buy a machine (ATV or Car/Truck), the first thing I do is a full fluids change (or at least Tranny fluid check/inspection). Just so I have a "warm fuzzy" and a good starting point to base my maintenance from.
But on an ATV I'd surely change the following (and my personal advise/opinion.... for what it's worth).....
1) Engine Oil and Filter - Pick your favorite flavor..... any "good" synthetic at or very close to manf. recommended weight. (Many here either use Polaris 5W50 or Mobil 1 0W40 and either the Polaris filter or "Good" aftermarket brand - For me it's Mobil 1 & Purolator).
2) Front Diff & Hubs - (The vast majority stick stricktly with Polaris brand fluids.)
3) Rear Diff & Trans (Here again you'll find the vast majority stick stricktly with Polaris brand fluids.)
4) Fuel - On that age and low mileage..... you may want to drain/suck out the fuel and put in new fresh fuel. ( I always add the recimmended dose of "SeaFoam" to my gas cans and/or tank to keep things stable and clean!!)
5) Air Filter & Pre Filter - At a minimum at least inspect and blow off any dust if fairly clean.... if dirty replace.
6) Spark Plug(s) - Kinda a PITA to change..... see how it runs, change if it runs rough or starts hard after all else of the above has been completed. (If used - allow the SeaFoam work it's "magic" for a couple rides first!!)
7) Anti-Freeze & Brake Fluids - Though it would be a good idea to change..... at a minimum inspect, test (anit-freeze) and top off if needed, with recommended flavor of your favorite brand.
8) Inspect Belt & Clean Clutches - Just remove the clutch cover and blow the cluches out with compressed air and inspect belt edges and sheave surfaces. (But at 140 miles..... may not be worth it, but good "learn your machine" experiance and bonding time!!)
9) Grease all Zerks - Use a good suspension grease and give them a few pumps. For the suspension bushing zerks, until you see the old squeeze out! (I'm personally a Mobil 1 fan.... so I used the Red Synthetic stuff!)
10) Check Electrical - Always know your machine.... check all lights, switches and levers for propper function!!
11) Owners Manual -
Read it.... or at the
very least skim it!!! (Touch on the
"hand control functions" for sure!!)
Really isn't anything special to look out for..... Ride and Have Fun!!! If anything breaks..... fix it and continue to ride and have fun!!!
Side Notes:
1) Use
Low Gear if
@ or Under 10 mph!
2) Shift gears from a
complete stop!
Here are a couple helpful links

.....
http://gh-ftp.com/ORV%20Manuals/Polaris/Sportsman/2004/2004%20Sportsman%20700%20MV%20-%20SM.pdf -&-
Index of /ORV Manuals
Enjoy!!!!