First, check the to-do list to see what is done and what needs to be done. For the most accurate version, check the website.
Second, check the /extra folder to see if there is a WIP.
Third, make sure that if you take art from somewhere, check its license first! You should also cite any sources you used, especially another HRP tile.
Fourth, do not use any of the original 8-bit art in your final products. You may use the art as placeholders, but do not leave it in the final product. The exception to this rule is when a complex object (such as an enemy) has not been re-done. It can be added to the interim release version. However, once a replacement has become available, then you must use it instead of the original.
Fifth, make sure textures are exactly 4 times the original size of the tile. In most cases, you should end up with a power of 2 texture (256x256, 512x512, 1024x512, et cetera). However, if the original art has a weird resolution, then you should use the original x4. Model skins should be power of 2 as well. It might work better for you if you created the tile in x8 scale.
Sixth, post the artwork at the Duke4.net thread. If you do not have an account, e-mail the artwork to me (Hendricks266). Tell me what you would like to be credited as.
Last, remember to back up your source .psd/.xcf files, and your source models. It will make the above rules much easier.