I second the Iberia or Carthage strategies. I can only think of four stragegies which may work for the berbers, listed in the order of efficiency IMO, with the most effective first:
- carthage - explained by others above. Strength is that you'll defend your starting desert provinces by this offensive, and push into strong roman heartlands, for instance Rome, where you have good troop buildings. Weakness is that the resistance may grow quickly, as romans can reinforce the area with troops trained in these heartland provinces with good troop buildings.
- Iberia first - explained by others above, having an army with many, at least 2 IMO, horse archers is recommended for this. Strengths: you'll meet quite weak opposition unable to defend well vs horse archers, Weaknesses: 1. there's a lot of WRE troops in Spain, so you may run out of archer ammo in the battles unless you have enough horse archers. 2. your abilities to defend your desert provinces are limited, but it takes long time anyway for the WRE to prepare for an effective offensive on these desert provinces even if you leave them almost unguarded. If you're quick in Spain, you might be able to reinforce them in time, and take Carthage pretty soon. 3. Spain is larger than the WRE controlled area in north africa. It's easier to reinforce the area, as no ships are required. It can, if you have bad luck, result in heavier fighting than the Carthage first strategy.
- rushing lepcis magna with a good army. This will help economy, and WRE will usually not handle their counter-attacks from Carthage well, which opens a path for taking carthage. If they camp in Carthage, you can improve your army somewhat and send all you got to Carthage, and should be able to take the city. Lepcis magna first strategy has the weakness that it takes longer to get an army there than carthage, so you'll have more debt by the time you get there.
- Sardinia first strategy - has same strengths and weaknesses as Lepcis magna first stragegy, but an additional weakness in that it might cut off good troops because your naval strength is very limited, and it's probably one of the least useful strategies