Melissa Kaplins website is amazing and will provide you with a TON of info. I would also purchase her book Iguana's for Dummies as it provides detailed, but easy to follow, information on iguana care.
For starters makle sure your new iggy is house appropriately in a large enclosure or room. He needs a basking spot he can perch under where the temps reach 100-110degrees. His amient (general) temps in his room or enclosure can be around 80-90degrees. A variety of different perches and basking branches will allow him to choose which temperature he wants to be in. A UVB light is very important, zoo-med and repti-sun 5.0, 7.0, and 10.0 are great bulbs. Your ig needs to be able to get within 6-10inches of these and these bulbs need to be replaced every 6months. A large tub for bathing, soaking and swimming should be provided. You can also allow your iggy to soak in your bathtub filled with warm water, be warned that they tend to poop when in warm water so the tub will need to be thoroughly steralized afterwards.
A good diet is important including a staple of dark leafy greens (collards, mustard and dandelion greens, endive, escarole etc) additional veggies, fruits and flowers can be added as "spices" such as shredded purple cabbage, shredded carrots, red, orange or yellow peppers, pod peas, squash, banana, kiwi, and rose petals. Supplementation with a good calcium supplement and vitimin supplement is important as well.
I agree with melissa, your ig really should be checkd out by a qualified herp vet, especially if you doubt his previous care was adequate. Bring a fecal sample with you as this will eliminate your worries that he may have any parasites.
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0.1 mexican Black kingsnake
1.1 Leopard Gecko's
0.0.1 Tokay Gecko
1.0 Blue Tongue Skink
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0.0.1 Red Tegu
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4.1 Cats