Looking for some painting and sewing tips? Look no further! Keep in mind that most of the things I'm going to share with you here I learned through trial and error. Patience is key if you plan on doing any kind of custom work, and my goal is to give you some pointers that would have helped me immensely had I known then what I do now. Frankly, I'm too lazy to organize all this into some kind of formatted list, so bear with me as I unload a stream-of-consciousness advice storm on you.
First, painting tips! The key to getting good results with anything you paint is, of course, patience and a steady hand. You should also make sure you have the right type of paint. For plastic (such as on figures), always, always, ALWAYS use acrylic model paint. I swear by Citadel Colour as it's the best I've ever worked with and their broad range of colours can't be beat. Most of the stuff you'll find in the modelling section of Wal-Mart or whatever is usually enamel paint. This stuff will never dry once you paint it on your figure and remains tacky forever. Also, it slowly eats away at the plastic over the course of several years. You want to protect your hard work, so use acrylic model paint. Also, beware of the acrylic paint that they sell in the craft section of some stores. It usually comes in a squeezable plastic bottle. Yes, it's labelled acrylic, but it's not model paint. This stuff will wear off really fast. Stay away!
Another key to successful painting is to have good brushes. It's definitely worth it to invest in a decent-quality brush that won't shed hairs into the paint as you work. Dollar store brushes are garbage. You can pick up some decent ones at an art supply store for maybe a couple of bucks each. Additionally, you may want to try using several different sizes of brush. I find that using a small, thin brush lets me get more even coats as well as saving paint. Naturally, you can also get more control and be able to reach tighter places using a smaller brush. If you have a lot of area to paint, though, a bigger brush will definitely save you a lot of time. That said, don't just dunk the entire brush into your paint pot and slather it onto your work piece. It's a waste of paint. Just wet the tip enough to work and dip it again when it runs dry. If you soak the entire brush, the paint will be absorbed into the brush itself and just dry inside there. It's not worth it. Another paint-saving tip is to do multiple thin coats, allowing time for the paint to dry in between each application. If you slather on a thick dollop of paint, it will not only take ages to dry, it is also more prone to rubbing off and, if you touch it before it's completely dry, you'll leave a nice big fingerprint on your work. Multiple thin coats also allow for a smoother finish, and you can more easily correct mistakes along the way.
Lastly, when all your painting is done, it's a good idea to seal your work with varnish or some other kind of sealant. I personally prefer the brush-on kind as aerosol sprays also never dry on certain kinds of plastic. A sealant will protect your piece from chips and scrapes and also does a wonderful job of evening out the finish on your paint.
Sewing advice is a little harder for me to give as I find it pretty easy and straightforward to do as long as you know how to thread the machine. The one tip I can think of off the top of my head is when you're working with stretchy material like T-shirt cloth, I found that the needle used to push the material down into the innards of the machine and gum up the works. The solution that I found to work really well is if you place a piece of paper under the material, and sew through that. When you're done, you can just carefully rip the paper away and you're left with a neat, clean row of stitches with a minimum of fuss.
Also, when sewing on a smaller scale, remember that every stich counts. One unravelled stitch can spell disaster for the structural integrity of your entire scale garment. This is why I always tend towards oversewing, that is, going one or two stitches further than I have to, in order to make sure the pieces are connected. Also, when you cut the thread off from the sewing machine, leave maybe two inches attached to the work piece so that you can manually tie a knot or two to keep it from coming apart.
I hope you've found these tips helpful and informative. I'll add more whenever I can think of them. Until then, if you have any questions, feel free to contact me using the link in the menu above. Good luck and happy customizing!