SMD parts cover a spectrum of sizes, from SOIC and 1206 that are relatively easy to use to ones that are really quite challenging. For resistors and capacitors, I use 805's when I can. Anything smaller is just too hard for me to hand solder.
With that introduction, I think 0.031 is a little big for the smaller stuff. It is fine for SOIC, but for 805's and smaller IC packages, particularly ones without pins that stick out, I prefer 0.015. I use Kester 44 (mild) rosin core flux and keep a tin handy. I makes a nice temporary paste to hold things in place and solder flows really well. I have tried some of the water soluble and no-clean fluxes, but didn't like them as well. Washing off residual flux after soldering is no big deal in my opinion. It also gets rid of fingerprints and other contaminants.
John