Decorative pieces may look disordered even when you are using a precise cutting style or a glue line that goes in a clean and straight manner. Sometimes the issue is not placement or technique; sometimes the issue is color. Sometimes you may have a bright paint, a single piece of patterned paper, a fabric scrap, and a couple of beads; all of these may appear individually fine, but they may also all be vying for attention in the project you are creating. If everything is a main event, then your card may not be a card, your ornament may not be an ornament, your panel may not be a panel, and your wood block may not be a wood block.
You will want to have a plan before you begin. Before you begin to cut, glue, or paint, you will want to establish a color scheme so that the project itself has some limitations. If you are working on your first decorative craft, perhaps pick a primary, a secondary, and a tertiary color. Primary colors will cover the biggest areas of a project, such as the painted background or the backing card or the fabric. A secondary color will be used for a border, the cut-outs of the paper, the thread wrapping, or a stencil shape; a tertiary color will be used very lightly, like a few dots, a bead, or some clay detail, or you could even use it in an edging.
You may find that the easiest way to do this is to have everything in front of you before you cut, and arrange it in front of you before you cut, so that you may choose those three shades from the materials themselves. Set your paper, fabric, paint sample, thread, and any beads in front of you on a plain surface, take a step back and see which one your eyes notice first, and when you notice two or three things at once, you will want to put some back; you do not need all of your favorites. What is needed is a relationship between all elements: surface, decoration, finishing touches.
Make a simple color swatch prior to the final arrangement or composition. Dip some paint onto a scrap; put some paper next to it and the fabric (or some thread); if you want a bead or clay detail, put that next to it too; make a decision about how to do that before you glue or paint the actual project; wait until your paint and glue have dried before you judge this; wet acrylic may paint stronger and some paint may appear paler, and certain pieces of paper may change shade when wet and glued down. Do this, because you may find you have made a mistake, because the final result is dry.
One of the more common things people do when fixing a weak palette is add more decoration; sometimes you paint a background and it looks flat, so then you decide to add a few dots; sometimes you paint a border and you decide that it looks plain, so then you may decide to put a second decoration on that; sometimes you feel that your colors just are not connecting and may decide to put on something new to tie them together, but this can just make it feel more cluttered. A better way is to take a color and repeat it somewhere; perhaps you may have something like a blue border and a blue thread wrap to tie it; maybe you may have something like an off-white paper cutout that ties in to something like a small clay detail. Repetition allows your eye to connect the dots.
You also have to keep texture in mind here. A flat piece of fabric scrap can look softer than a flat paint of a certain color; a flat piece of paper can look uneven than a smooth paper; or beads can look brighter than the rest of the project when placed in the final arrangement because they may be reflecting a little light. Sometimes, when working with textures, you actually want a more limited color scheme; sometimes you just have too much texture going on, or a pattern may repeat, or you are just layering a bunch of paper; if you have a lot going on in terms of the surface, or if you have a lot going on in terms of the decoration, then you may want to just do fewer colors.
Before gluing anything down, arrange your final palette into the final placement and see if it works; arrange your primary color, secondary color, and tertiary color onto your final layout, and if your tertiary color is placed everywhere and your secondary color is actually your primary color, then you will know something has gone wrong. You have a successful palette if your shapes are easy to recognize, your decoration works on them, and your detail works on both.