I strongly believe that no matter the level of your painting skills, or the detail you want to put into your miniatures if you your basing is rich, layered and consistent then your army will look amazing!
The basic tenants I follow when basing my models
I use rich colours, with plenty of contrast from from basecoat to final highlight.
I use strong heavy textures, most pastes or textured paints don't cut it here.
I make sure the edges contrast with the final highlight of the base.
I use a variety of grass, flowers and flocks to reinforce the battlefield theme of the base.
Now I realise this all seems rather obvious but for a tabletop gaming army you need to be bold and small details can end up looking muddied and lost at a gaming distance.
I cover the base in PVA glue and dip the model in medium grain sand or scatter material, remove the model and shake/blow away the excess sand. I use a medium grain sand because too fine and it won’t take colours well when dry brushed, too heavy and it will look a bit odd... I have recently been using Army Painter 'Brown Battleground'.
I paint a layer of watered down PVA glue over the base to lock the sand down and stop it rubbing away.
I then paint the sand with watered down dark brown paint (in the very old days I used Games Workshop's Scorched Earth) water the paint down heavily and it will go onto the base really easily.
I then dry brush on a layer of mid brown, then desert yellow brown and then finally an ivory (and sometimes a very final white dry brush). This should give you a nice gradient of colour that doesn’t look too stark or bland. (Again, in the distant past I used GW's Bestial Brown, Snakebite Leather, bleached bone and sometimes Skull White.)
I then choose 2 colours of grass tuft and use a scattering of flowers, chosen to compliment your models colour scheme! I use green grasses on more temperate basing theme (in place of using green colours on the base) and if it is a desert I'll use brown grasses. Sometimes a mix of colours is used. Go crazy!
One final note
Whatever way you choose to base your forces, make sure you follow it religiously across every unit in your army. A unit is not finished unless the bases are finished. A basecoated unit with finished bases will look better than an unbased unit that is shaded and highlighted.
Even if you are just aiming for a three colours and done army, spend more time on the bases and it will still look great on the battlefield!
May your brushes always be pointy!