1. Caulk
Caulk is the most overlooked and inexpensive tool I know of. If you have an old house but the wood is good (not rotten), you will be shocked at what a few tubes of paintable caulk can do. Fill any cracks along baseboards, between trim, on edges of cabinets, and in corners. If you're a DIYer installing built-ins, trim, or cabinetry, you'll need it to finish your project before painting. Below is a cabinet corner before and after caulk.
I like the Alex caulk by DAP at Home Depot or Lowes which is about $3/tube, but use whatever you can find as long as it's paintable and fast-drying. Buy 3 or 4 tubes at a time if you're working on an entire house; you'll make use of it eventually, but it stinks to run out in the middle of a project. I like white more than clear so I can easily see where I put it after it dries (I'm going to paint over it anyway). We've brought some old, nail-hole-filled, cracked, dog-chewed, misaligned trim back to life in houses we've bought, and all with caulk and a coat of paint. Below is a baseboard before and after caulk.
To apply a caulk line like a pro, start with a tube opened with a clean angled cut off the tip, and load it into your caulk gun. Run a sparing line of caulk along a crack/crevice, and use a finger to swipe down the length of it in one smooth motion. If you didn't apply enough, you can always add another line of caulk and repeat. If you apply too much, you'll quickly have a (water soluble) mess on your hands - but nothing soap and water can't clean off your skin and tools. Just wear old painting clothes. Practice makes perfect!
2. Paint
At around $30 for a bucket of good quality paint, you can completely transform and renew a room. Here's an example of a bathroom completely transformed with paint (and some peel-n-stick floor tiles and curtains).
I usually avoid bright or intense colors in smaller spaces, unless there's wainscoting, and even then, I tend to err on the neutral side because you can always add color through fabrics, furniture, and accessories. And here's the rule: if you can clearly see it is blue or green or orange on the paint samples rack, it's going to be 10x more blue/green/orange on a wall. I promise. It will never be more gray on the walls than it is on the paint sample card.
Here's another example of how enormous an effect paint can have on a space. At each step in the process of renovating this kitchen, paint played a big part. I loved that blue...I loved it with the warmth of the wood cabinets.
Choose a color you love, then ask yourself, "Is this a wall color, or an accent color?" Wall colors take more effort to change than accents like upholstery, framed art, or painted wood furniture. And they affect your space with far more ferocity than a smaller item of the same color would. The blue color in this kitchen made the space feel eclectic, cozy, and artsy. The light gray in the next photo made it feel more light, clean, and probably appealed to a wider audience (which is why we painted it gray when we sold it).
Once you decide your chosen color belongs on your walls, go 2-3 steps more gray with it. Then take several choices home as paint samples, tape them to your walls in the rooms you mean to paint, and live with them for a few days before deciding. It might be more time than you expected to spend in preparation to paint, but you'll be glad to avoid having to start over. Don't skimp on the brush, unless you're painting something heavily textured like old metal scrollwork. I love my 2" angled tapered Zibra brush, and it's lasted through painting many rooms. It'll cut a line cleaner than any paint tape could give you, with way less trouble. I don't use tape anymore - use a practiced, smooth motion, a quality angled brush, and clean up any overpaint on glass with a razor. Where two colors meet, always paint the darker paint last, as it'll only take one coat to cover any overpaint from the other color. If you're unsure whether you'll be painting over oil or water-based, use the rubbing alcohol and cotton swab method. If it's latex paint, it'll come off on the cotton swab. If you're going to use a water-based paint, which dries faster and has less fumes, you'll need to prime first if the swab is clean (which means oil-based paints were used).
3. Fabric
Fabric adds color, pattern, and texture. It softens and warms a place. One gal who knows this well is
The Nester, a.k.a. Myquillyn. Please take a look at her site (click on either photo below too) - it is a wealth of smart decorating knowledge.
Can you believe that's a drafty addition to their barn? Look at that soft, inviting bed and the sheep skin rug.
Can you believe that's inside the barn?? She achieved this cozy look with fabric - curtains, upholstered furniture, bedding, rug, pouf, and pillows.
Fabric can be added as slipcovers, rugs (they're textiles too!), simple drapes, bedding pillows, to the back of bookshelves, to the walls themselves...there are so many ways to add fabric. Layer rugs if you have multiples, like jute under woven, or cow hide over wool (if you are lucky enough to have a cow hide rug). Add a fake fur throw or a sheep skin. Layer bedding with a bedskirt, coverlet or quilt, throw or blanket, and coordinating sheets. Make your bed beckon to you.
You don't have to overpay to make your space cozy. Some Walmart stores still sell fabric by the yard for around $3, and fabric stores have clearance racks. There's fabric.com and overstock.com. Yard sale pillows can be recovered, and flat sheets or drop cloths can become curtains. Remember to hang your curtain rods (including shower rods) as close to the ceiling as you can, and as wide as you can, so when they are open you can allow ALL the light in through the window and not cover any of it except the window's trim on the side. This lengthens the space and makes the window seem bigger.
To make simple curtain panels (and some links to tutorials)...
With a flat sheet: snip the seams on the left and right of the thickest hem (usually goes at the top of the bed, where your face and hands are), leaving a tunnel to slide a curtain rod through. Or use clip-on rings.
The Frugal Homemaker
With fabric by the yard: fold the raw edge twice and iron. Use fusible hem tape and an iron, a hot glue gun, or a sewing machine to secure. Fold one side's hem thick enough to fit a curtain rod through or use clip-on rings.
Two Twenty One
With a drop cloth: choose a size appropriate for your window, and use clip-on rings. Alternately, cut a larger drop cloth in half to save money, and finish the raw edge with a seam or hot glue or fusible hem tape.
Better Homes and Gardens (several tutorials on this one)