I'm a pretty low level (13) and relies mainly on Tier one troops. Mortars are Tier 1 troop's worst enemy and the people I attack are usually 3-4 levels ahead of me which means they already have some mortars. They usually devastate my army before my army gets in. I spread out my troops but they get killed separately and I still lose. How to avoid this?
Speading your troops out and delaying them so there aren't large groups in one place at one time will help. You don't have to deploy them all at once. Giants can withstand a few mortar hits and are very effective against mortars. Mostly, target selection is critical for players of all levels. Look for full elixer pumps that are outside the walls. Then level up your barracks and troops as fast as you can. Elixer fuels offense. Good Luck.
If you realy on tier one troops, I'll just use 100% goblins. Goblins are fast and can avoid bombs and spring traps (and mortars sometimes). Once you get giants though, destroying mortars gets easier and you can use giants as "meat bait". take a look herehere
Use half archers and half barbarians. Deploy your barbarians first as meat shields, then spread out your archers behind them. If people you attack are always 3-4 levels ahead of you, you may want to consider dropping to a lower trophy level in order to meet more appropriate for your level opponents