ABC: Always be coding
Know thy complexities ( Read this cheat sheet. ) Then make certain you understand how they work. Then implement common computational algorithms such as Dijkstra's, Floyd-Warshall, Traveling Salesman, A*, bloom filter, breadth-first iterative search, binary search, k-way merge, bubble/selection/insertion sort, in-place quick sort, bucket/radix sort, closest pair and so on. Again, ABC.