What do you want to export? - be aware of export scope e.g. meshes, cameras, lights, animation rigs, etc.
Applications often let you export selected objects or a whole scene
Make sure you are exporting only the objects you want to use from your scene by either exporting selected, or removing unwanted data from your scene.
Good working practice often means keeping a working file with all lights, guides, control rigs etc. but only export the data you need with export selected, an export preset or even a custom scene exporter.
What do you need to include? - prepare your assets:
Meshes - Remove construction history, Nurbs, Nurms, Subdiv surfaces must be converted to polygons - e.g. triangulate or quadrangulate
Animation - Select the correct rig, check frame rate, animation length etc.
Blend Shapes / Morphing - Make sure your Blendshapes (Maya) or Morph targets (Max) are assigned / set up the export mesh appropriately
Textures - Make sure your textures are sourced already from your project or copied into a folder called \textures in your project
Smoothing - Check if you want smoothing groups and/or smooth mesh
How do I include those elements? - check the OBJ export settings
Be aware of your settings in the export dialogue so that you know what to expect and can match up the obj settings In Modest3D
Check Animation / Deformations / Skins / Morphs as appropriate
Cameras and Lights are not currently imported in to Modest3D but cameras and lights can be created and edited in Modest3D easily
This is an example of 3DS MAX OBJ export best practice:
After the model is complete and optimized to game ready status
Center the model to the 0,0,0 position in the 3d world