First, let´s talk glues (or adhesives) because depending on what you are glueing down, you need different adhesives.
Below is a description of the ones I use, there are of course hundreds of brands out there but for me these have become favorites.
Aileen´s Jewelry Metal Glue – this glue is outstanding for glueing down metal pieces on your canvas. Mind you – not the really heavy stuff – for those you really need a 2 component adhesive. This glue is not thin and runny like super glue. It is more like a gel. I use a spatula or dip the back of the piece that is to be glued down. It dries almost instantly when put down.
Mod Podge – this glue is great for glueing down paper, for decoupage and for sealing photos. You could use it for paper flowers etc also but it dries too slow for my taste so I rarely use it for other than paper and decoupage. Mod Podge comes in Matte or Glossy. It is quite thin so I usually use a paintbrush for application.
Finnabair´s 3D Gloss Gel from Prima Marketing – This glue is thicker than Mod Podge and stickier. Perfect to use on glueing down pieces of wood, plastic, resin, clay etc. As it is thick I use a spatula or my finger when applying to pieces.
Glue Gun – when I first started with Mixed Media Assemblage I used the gluegun for everyting. With time I got wiser because, this is not something that keeps over time. I started noticing flowers and embellishments falling off after some time. So these days I only use the Glue Gun when glueing down flowers and lace on a canvas.
Super Glue – Sometimes you need an adhesive that is really fast. The super glue is perfect for that, but even though it sticks immediately it really doesn´t mean it sticks for long. I´ve had pieces falling off my canvases using the super glue so only use it for really light stuff.