If you are a worldbuilder or mapmaker working at a global scale, it can be helpful to have an actual globe to guide you. If your world is an alternate Earth, then you are in luck. You can go to Amazon or troll the thrift stores and garage sales for a cheap globe of the Earth. All done.
For the rest of us, the globe we need cannot be found in any thrift store. So we make our own.
The above is an 8 inch desktop decorative globe I bought at a furniture store. Globes run for about $15-$30 at stores, or cheaper if you can find them used. What you want is a sturdily built globe with no raised relief.
Accuracy is not important. Any out-of-date borders and countries will be slathered over with a couple coats of gesso. Gesso is a type of acrylic paint that creates a toothed surface that can be painted on. You can buy it at any art store in bulk for pretty cheap. It's a good thing to have around.
Next, use a pencil to outline where your continents are going to be.
Fill in the oceans with a base color. This will provide contrast between land and sea, making the next step easier.
For raised relief, use a heavy molding/modeling paste. This is where you will be defining your coastline and texturing the landscape. I would recommend making your coastlines more fractal than this, as mine are too smooth, but it's too late to change that now. Refer to this Cartographer's Guild tutorial
for creating realistic coastlines.
Mountains. They can be raised with a touch of the finger, keeping in mind that the paste will shrink as it dries. Exaggerate your peaks and use water to smooth out plains, deserts, and valleys.
After the paste dries, paint the continents with acrylics. My planet has red and black plants, hence the color, but the technique is the same. Refer to tutorials on painting landscapes for getting a realistic color into your lands. Take advantage of the texturing you created earlier. Lightly dry-brush a light gray (not pure white) onto your mountains to add a dusting of snow to the peaks. Dry-brushing is a technique used by modelers to create weathering effects and make things look "dusty." To dry-brush, dip a dry brush in thick paint and wipe off most of it on a towel. With what remains, lightly drag your brush across the raised surface of your mountains in multiple directions. This should be your last step, after you've added all other layers of color.
A wash is sort of the opposite of dry-brushing. Dilute a dark color in water and let it sink into the nooks and crannies of your textured surface. Wipe off the excess with a towel. Dry-brushing makes highlights; washes make shadows.
Now that you have your mountains, decide where your lakes and rivers are going to go. Keep in mind that most rivers won't be visible on the global scale, unless your globe is very large. In the above image you can see that I used natural depressions in the texture to make my lakes. Refer to this tutorial
on realistic placement of rivers.
Lastly, paint the ocean. Look at pictures of the Earth from space to get an idea of the range of colors you will be using. Shallows tend to be lighter and greener, while areas with red seaweed and red algae will be brownish. The reddish swirl at the center of my globe represents a thick layer of vegetation, "plantbergs" of sorts, in case you were wondering.
Sea ice. It's bluer than snowpacked land, which I exaggerated here to make the continents more visible. Most of you will be placing the ice at the poles, obviously. This is a tidally locked planet, so an entire side is hidden away from the sun and therefore very cold. Determine your world's weather patterns and sea currents before painting in the ice.
That's it! A globe is very handy to reference when making maps of your world. Plus, it'll look nice on your desk.