Well, the title says it all!

I have a tank and I want to make a flag hanging from the turret following the shape of the armor. Ive tried a few things (candy wrappers dipped in glue for example) but I have yet to get a good result!

Can someone please give me some pointers?

//I

Try tea bags or tissue paper dipped in whiteglue/water mix.
Drape it over the armor till it drys. Then gently pry it off and you have a nice firm flag to paint as you like.

Another material is the tissue paper commonly used in gift wrapping as 'filler'.

Find the flag you want online or scan it. A flat, unfurled image is best, the larger the better. Save it as a Jpg file. Import it into a word document as you would a piece of clip art. Resive it. Chose print from the File command and set the printer properties at maximum. Print the image on plain white paper. Allow the inks to fully dry an hour or more. Seal the image with MicroScale Decal Saver. Let this dry, usually 15-20 minutes will do. Use a straight edge and sharp #11 to cut out the flag. Apply a layer of diluted wite glue to the back side. Let this soak in fro a couple minutes as the paper becomes softer. Lay the flag where you want it and gently press it down to match the contours. You can add highlights and shadows as needed.
The good things about this process is you can save multiple impages which are always consistent, cost runs to ink and paper, and you can print multiples on one sheet of paper.
To add a backside, you have to determine how the two sides loko, does the image appear reversed or is there even a different image on the back? Once you find out, you can join the two sides in your photo editing program and create a two sided flag the same way. Just get a sharp crease before applying the white glue and lay in nice furls befroe the glue dries.