Very first jobs.
1) I'd say the day you pick up the dragon and it's viv, replace the substrate and replace the uv globe or uv tube ( they are likely inadequate / dodgey / too old or all these). See my cheatsheet for hints :
viewtopic.php?f=6&t=234738&p=1806050#p1806050
Very least a 26W UVB200 , ensure it's not obstructed by a mesh screen , in a reflector (dome or hood) and no more than 8 inched from the beardie's basking spot. A T8 10% - 12% UVB is better , needs to be mounted under the lid in a reflector hood, Even better is a T5HO 10 - 12% UVB is super , again in a reflector hood and best under lid.
Note in my Cheatsheet the dodgey brands to avoid.
2) fridge style digital thermometer like this :
http://www.ebay.com.au/itm/4x-LCD-Digital-Temperature-Thermometer-Fridge-Freezer-Aquarium-Fish-Tank-Reptile/152552282270?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20140107090050%26meid%3Db2eb761dc4be4193a60311fb6239b157%26pid%3D100011%26rk%3D2%26rkt%3D12%26mehot%3Dpp%26sd%3D331726814386&_trksid=p2047675.c100011.m1850 , much better that stick on analog bar and dial style thermometers , and cheaper.
3) Do not believe anything the seller tells you about it's health status, find a local reptile / herp vet and have the vet do a wellness assessment and take bloods , fecals, and an x-ray.