Being, like the mariner, a man of infinite resource and sagacity, I agree that the bestowing of such information upon the populace of these here esteemed forums would be to the benefit of all, so without further ado, I shall lay out the steps required to achieve a bond of such baby-bottomed smoothness that even the daemonettes of Slaanesh should weep in awe.
hum...
aaaaanyway, here's stuff I know about glue n fings.
1) a small bond (e.g. an arm onto a mini)
If metal or resin is involved, you want to use superglue. If the limb is big enough (e.g. a space marine arm) then pinning it can be very helpful indeed, and greatly strengthens the bond. Use a wee bit of blu-tac to locate the holes correctly. (Pinning: drill small hole in part A. put small piece of blue tac on part B. Press Part A in place. remove part A carefully. The resulting little sticky-uppy-bit on part B is where you want to drill the hole into part B. Do so. Cut small piece of wire to fit the hole in A and B. Glue A, B and wire together) If it's plastic to plastic, then use polystyrene cement (aka the sensibly named "plastic glue")
2) a big bond (e.g. a dragon's wing to a dragon's body)
Treat as a small bond, but definitely, definitely pin it. Double pin if you can.
3) a gap that needs filling (e.g. if you stick a dragon's wing on but you bollix it up and end up with a 1mm or 2mm gap between the wing and the body)
This assumes that the part is already pinned and glued on. If so, get some gel type superglue. apply generously so it fills the gap, but doesnt squidge out too much elsewhere. A wee bit is OK. Next, dump a load of baking powder over the glue. This will get fecking everywhere, but you can just blow it off. You'll be left with a kinda whitish crustiness filling the gap. This bonds things incredibly strongly, and is itself eminently sandable to a very smooth finish. This is especially helpful for tanks.
4) a big ol bugger of a gap.(3-10mm or more)
Use milliput. Fill it in as best you can, but dont overflow the gap. let it cure. Come back the next day with milliput and now smooth it out as best you can with a damp finger. To finish, get a wet finger and smoosh it across the surface. Uncured milliput is water soluble (unlike GS) so by doing this you actually work up a kinda slurry on the top. This is really easy to spread so finely over the surface that there is no visible join between the 2 parts and the gap-filling milliput. A quick once over with sandpaper once dry, and robert's yer muvver's bruvver.
5) For a rust effect:
If you want a crusty rust effect (like my nurgle tanks) you can use superglue for this.
Apply superglue and squidge it randomly into the approximate shape of the desired rust patch. Dump baking powder on it. Blow off the powder. Now, paint the whole shebang a dark reddish brown. When dry, put masking fluid over the rusty bit, leaving the very edges uncovered. Paint the whole mini your desired colour. (blue for ultramsurfs etc) Highlight and finish as usual. Now, remove the masking fluid. Add some rust coloured pigment to the rust. Seal with pigment fixer.
If anybody has any other genius uses for glue, please feel free to add em