Hey there Razz 
a few ideas on painting…
As a fair bit of my recent work has been in Acrylics, I thought I’d start there… basically traditional painting can be approached in as many ways as there are artists… yet a few hints and know-hows about how each medium works can help you achieve the results you want.
As Goache is almost like a step inbetween watercolour and acrylics… you can apply some of the ideas to goache as well - it dries as fast… if not faster than acrylics, difference being that it dries matter than the acrylic paint. Both are intermixable and versatile paints that can be used in many different ways (by intermixable I don’t mean actually mixing green from goache yellow and blue acrylic, although I’m sure that it’s been done by someone out there… 
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Acrylics can be used to apply washes / glazing; layering thin washes of colour on top of each other to allow for a transparency effect between the layers. This can be similar to watercolour painting, esp for artists that choose to work on paper. Main difference is that the colours become non-soluble once dried, so you won’t smudge or disturb the bottom layers by going over them. You can also paint in an oil-painterly style, using mediums (premixed liquids or gels designed to give you certain effects with the paints) that slow the drying process (as acrylics tend to dry quite fast…) and applying the paint thicker with brush or knife, moving the paint around on the canvas. You can also paint straight from the tube, although the thickening mediums make the paint last longer.
Depending on your composition (aim for simple effective compositions to start with, this will give you more freedom to experiment) it’s a good idea to with a brush roughly sketch the shapes you are going to paint, allowing you to block in the composition of the entire painting at an early stage… Leaving the background to the very end can be a nightmare if you say painted a detailed tree or someone with dreadlocks… 
Many artists refuse to start with a white canvas… grounding the canvas in a neutral colour that will help pick up say skin tone or part of the foreground will give you a nice starting point for washes. There is nothing wrong in starting with a white canvas though, good to try both Glenn’s suggestion of doing thumbnails is a good and well practiced method, both for composition and for freeing up brush technique… the smaller paintings will allow you to experiment and push things further, letting you try several approaches with the “same” painting without feeling too precious about the result!
Keeping the palette to a minimum is good for starters… some advise to only paint greyscale to begin with… this gives you a good feel for values, yet I totally understand the need to apply colour. Learning the cold / warm colour scheme is also good, this gives you more control when mixing colours. This link has some good advice on how colours work: http://painting.about.com/od/colourtheory/a/Top_color_mix.htm
With acrylics I find that using a mist spraybottle both on the palette and on the canvas, gives me quite a bit of extra working time. I use a standard acrylic painting medium - mix with the colours to get the right consistency: to slow the drying time further I use a drying retarder… VERY small amounts, anything over 5% in the paint can make it soluble. I don’t tend to use drying retarder that often, yet it can come in handy. Apart from that there are modelling compounds, gel mediums and pastes that you can apply to the canvas (or painting surface of choice) and then paint over - or mix with paint and apply… these mediums give you that thick layered effect. You can also add sand and other materials to your medium for a gritty or 3D texture. There are spreader mediums to help spread large washes evenly acoss the canvas, really when you start looking there are mediums on the market for every kind of brushstroke… Matt medium, glossy, marbing, antiquing… etc. You don’t need them all: I find that water and standard acrylic medium (50-50) works very well
In acrylics you can work with either a hard-edge style or blend the colours into each other. When blending it’s easiest to do this while the paint is still wet. for a more “painterly” style; rough brushmarks will give that blended and free look, for more subtle blending a fan brush comes in handy, as you can blend colours without leaving visible brushmarks.
Working dark to light is generally the way I paint… also using the colours in the darkest areas to create the midtone shadows (rather than using black if that makes sense…) Like in this one: click here I have used the green in background in the shadows on her face - and the choice of background colour was helped by her green eyes…
Hope there are some things in here that make some sense… if you have questions do fire away main thing with painting is that you enjoy it! experiment with colour and value and composition, see how your colours look when placed next to each other, play around with thinkness and texture. I am sure you will fly!
take care and cheers
a.
