If you are still using the sponge applicators that you sometimes get in eye shadow palettes, do yourself a favour and throw them away. They make applying makeup harder, not easier. Why brands continue to produce these is a mystery when anyone who's stumbled across a YouTube tutorial knows that makeup brushes are the key to a better result.
You don't need to spend hundreds on MAC or Shu Uemura brushes (though they are a great investment), but it really is worth building up a small collection of decent-quality brushes from a brand like Real Techniques or Eco Tools. Which ones to pick depends on which type of makeup you like to wear, but a good starting point would be to buy a good blusher brush, a medium shadow brush and a crease brush, an angled brush for liner and/or brow powder, and something to help you apply foundation. If you fancy a brush, try the Bare Minerals Face Perfecting Brush (£24), which has a shallow cutout section in the middle to help get around curves and creases. If you'd prefer to apply with a sponge, the Beautyblender (£16) is worth the investment.